The head and neck is the upper part of the trunk. Skull forms the skeleton of the head. It is a bony box. The main function of skull is protection. The brain is protected in the cranial cavity. The anterior part of the skull forms the facial skeleton. It lodges the sense organs and the receiving ends of the respiratory and digestive system. As you can feel, note that there is a thin area between the skull and the skin. In our dissection we are studying this area under the superficial dissection of the head. The skull has only one movable bone, the mandible. This bone articulates to form the temporomandibular joint. Muscles which act at this joint form the temporal and infratemporal regions. The eye, ear, nose and mouth along with their associated structures are located within the bony box, the skull. All these structures are studied under the heading deep dissection. Most of these being midline structures they are studied in sagittal section.
The neck is the part connecting the head with the thorax below. The cervical vertebrae form the axis for this. The prominent sternocleidomastoid muscle forms as a landmark to separate the neck into two triangles, a posterior muscular part and an anterior visceral triangle. The posterior triangle is made up of musculature spanning from the vertebrae posteriorly to the scapula, clavicle and the ribs laterally and inferiorly. It is wider inferiorly. The viscera are lodged in the anterior triangle. It is wider superiorly and narrower inferiorly. The neurovascular bundle lies between the musculature and the viscera (Fig. 1).
SUPERFICIAL DISSECTION OF HEAD
Scalp is the region on the top of the skull. Anteriorly it extends up to the superior orbital margin. Here the forehead is included. Posteriorly it extends up to the external occipital protuberance and superior nuchal line. Laterally it extends up to the zygomatic arch. The scalp is made up of five layers—skin superficial fascia with neurovascular bundle occipitofrontalis muscle, loose areolar tissue and the pericranium.
Norma Verticalis (Fig. 2)
This is the external surface of the skull, viewed from above. Note the following features:
Frontal bone: This occupies the anterior part of this region.
Frontal tubers: These are the prominent elevations on the front. These are more prominent in females
Parietal bones: They occupy the central part of the norma verticalis. Note the emissary foramen. This permits the emissary veins.
Parietal tubers: They form the lateral prominence on the parietal bone.
Coronal suture: This is where the frontal bone meets the two parietal bones.
Sagittal suture: This is where the two parietal bones meet.
Lambdoid suture: This is where the two parietal and the occipital bones meet.
Occipital bone: This occupies the posterior part of the skull
Vertex: This is the midpoint on the top of the skull.
Norma Frontalis (Fig. 3)
Identify the following features on the skull in the anterior aspect.
Glabella: This is the midline elevation where the superciliary arches meet.
Superciliary arches: These are the elevations above the supraorbital margins.
Supraorbital margins: These are the sharp margins forming the superior border of orbit.
Supraorbital foramen or notch: See this nearer to the medial side on the supraorbital margin. It can be either a foramen or a notch on the skull.
Norma Lateralis (Fig. 3)
On the lateral side identify:
Zygomatic arch: This is the bony elevation felt between the lateral margin of the orbit and the pinna of the ear.
Superior temporal lines: Note these superior and inferior temporal lines above the zygomatic arch.
External auditory meatus: Note this opening in front of the mastoid process
Mastoid process: This is the bony prominence seen behind the auditory meatus.
Norma Occipitalis (Fig. 3)
On the posterior side identify:
External occipital protuberance: This is a prominence on the posterior aspect of the occipital bone in the midline.
Superior nuchal line: This is the line radiating from the external occipital protuberance.
Supreme nuchal line: This is the line radiating from the external occipital protuberance, but thinner and above the superior nuchal line.
SURFACE ANATOMY (Fig. 4)
- On the living feel, the supraorbital margins. The supraorbital notch can be easily felt on the living, but not the foramen.
- Feel the subcutaneous skull throughout the region. Note the frontal and parietal tubers.
- On the lateral side, in front of the external ear feel the zygomatic arch.
- Superficial temporal artery pulsations can be felt in front of the external ear, above the zygomatic arch.
- Feel the mastoid process behind the external ear, and the external occipital protuberance in the midline posteriorly.
The superficial fascia is fibrous, attaches the skin to the occipitofrontalis muscle. It is also firmly attached to the blood vessels. It has the cutaneous neurovascular bundle. They enter the scalp from the periphery and move towards the vertex. Nearer to the circumference they are deeper to the muscle. They pierce through the muscle to reach the superficial fascia. The arteries can easily be identified as they bulge. The veins can be identified by their blue coloration. The nerves accompany the blood vessels.
Cutaneous Nerves—Anterior Aspect (Fig. 5)
Supratrochlear nerve and blood vessels: These are fine branches located one finger breadth from the glabella.
Supraorbital nerve and blood vessels: Feel for the supraorbital notch or foramen trace the thick neurovascular bundle through the frontal belly of occipitofrontalis.
Auriculotemporal nerve and superficial temporal blood vessels: Feel the zygomatic arch near the pinna of the ear trace the thick anterior and posterior branches of the neurovascular bundle traversing to the vertex. It is easy to locate the artery, which is bulging and anterior most structure. The nerve is thick, behind the artery and deeply placed.
Frontal belly of occipitofrontalis muscle: This is relatively a thicker belly. It is inserted into the skin near the eye brow. It has two bellies, the right and the left. An aponeurosis can be easily seen between the two bellies.
Cutaneous Nerves—Posterior Aspect (Fig. 6)
A wide central area upto the vertex is supplied by the upper three posterior rami. The first cervical branch joins the second to form the greater occipital nerve.
Greater occipital nerve and occipital artery: These are seen one finger breadth from the external occipital protuberance. The greater occipital nerve is 0.5 mm thick and can easily be identified. Note the greater occipital nerve passing through the occipitofrontalis muscle. The occipital artery is tortuous and generally can be easily identified. It runs lateral to the nerve, gives branches to supply up to vertex.
Third occipital nerve: It is a small branch and supplies nearer to midline.
Great auricular nerve: Posterior branch of the great auricular nerve is seen in groove between the pinna and the mastoid process. This supplies the back of the ear lobule and the adjoining scalp.
Lesser occipital nerve: This nerve runs along the posterior border of the sternocleidomastoid muscle. Clean this nerve. It gives branches to the lateral aspect of the skin of the back. Branches of this nerve are seen between the above two nerves.
Occipital belly of occipitofrontalis muscle: This has two bellies, the right and the left. Identify this thin muscle belly arising from the supreme nuchal line. Occipital belly of occipitofrontalis is the muscle of the posterior aspect of the scalp. Trace these thin flat fibres from the supreme nuchal line to the vertex. Note the aponeurosis between the right and left bellies and also the epicranial aponeurosis between the frontal and occipital bellies of the occipitofrontalis muscle. The occipitofrontalis is a single muscle. This muscle along with the galea aponeurotica acts together to raise skin of the forehead. Perform this action on your body and feel the contraction of both the bellies of occipitofrontalis.
Galea aponeurotica: It is the intermediate aponeurotic part of the muscle, laterally merges with the temporal fascia.
Nerve supply: Both the bellies are supplied by the facial nerve.
LOOSE AREOLAR TISSUE
Turn the body back to the supine position and dissect:
Appreciate the vault of the skull here. It is covered by the periosteum. This periosteum is called the pericranium.
SKELETON (Fig. 7)
Identify the features on the articulated skull.
Glabella: This is the elevation in midline.
Superciliary arches: They extend out from the glabella.
Nasion: This is the depression on the bridge of the nose, where nasal bones join the frontal bone.
Cheek elevation: It is formed by zygomatic bone.
Maxilla: Forms a major part of the facial skeleton and lodges the upper teeth.
Symphysis menti: This is the part where two halfs of the mandible meet in the midline.
Angle of the mandible: This is the posterior sharp pointed end of the bone.
Orbital margin: This is formed superiorly by the frontal bone, medially by maxilla, inferiorly by maxilla and zygomatic bone and laterally by the zygomatic bone.
Nasal aperture: See that it is formed by the nasal bone and maxilla.
Infraorbital foramen: Note this below the inferior orbital margin.
Mandible: See the ramus and the body of the mandible.
Mental foramen: See this foramen on the mandible.
SURFACE ANATOMY (Fig. 8)
Identify the following on the living body and correlate it with the skull.
Palpebral fissure: This is the gap between the two eyelids.
External nose: This is formed by the bridge of the nose: This is the bony part of the nose, alae of the nose—feel them, they are formed of cartilage and the anterior nasal aperture—is the external opening of the nose.
Cheek: Feel the hard zygomatic bone beneath your cheek.
Maxilla: Feel the maxilla, note the upper jaw formed by this.
Mandible: Feel and move it in your fingers. It forms the lower jaw.
Oral fissure: This is the gap between the two lips.
Facial artery pulsations: Clench the teeth feel the masseter. Put your fingers in front of the muscle and feel the pulsations of the artery.
Superficial temporal artery pulsations: Put the fingers in front of the pinna of the ear over the zygomatic arch and feel the pulsations.
MUSCLES OF FACIAL EXPRESSION (Fig. 9)
The muscles of facial expression belong to the panniculus carnosus group of musculature. They control the orifices of the special senses. They have a bony origin and a cutaneous insertion, and so are capable of moving the skin of the face and scalp. Try to locate each of these muscles.
Muscle of the Eyelid
Corrugator supercilii: This extends from the bridge of the nose to the forehead. This produces vertical wrinkles of the forehead skin.
Orbicularis oculi: Identify this muscle within the eyelid. It is an elliptical muscle. It takes origin from the medial palpebral ligament. It has a palpebral part within the eyelids and this gently closes the eyelids. It has an orbital part which extends on to the adjoining orbital margin. This part screws the lids towards the medial side.
It has a lacrimal part which is attached to the lacrimal sac and opens the lacrimal sac.
Muscles of the Nasal Aperture
Compressor nares: This is seen on the bridge of nose.
Dilator nares: This is inserted into the alae of the nose.
Depressor septi: This is inserted into the septum from the maxilla.
Levator labi superioris alaequi nasi: This muscle extends from medial side of orbital wall to the alae of the nose.
All the muscles of external nose are small and have a limited movement in humans. They perform the movements specified in their names.
Muscles of Oral Aperture
Orbicularis oris: This is the sphincter of the oral aperture. It is an elliptical muscle extending from the maxilla to the mandible in the midline.
The following muscles stretch from the neighboring bones into the lips, like the spokes of a wheel and act as dilators.
Zygomaticus major: This extends from zygomatic bone to the angle of oral aperture.
Zygomaticus minor: This extends from zygomatic bone to the angle of oral aperture. This muscle lies medial to the major.
Levator anguli oris: This extends from below the infraorbital foramen to the angle of oral aperture.
Levator labi superioris: This extends from above the infraorbital foramen to the upper lip.
Depressor anguli oris: This extends from the mandible to the angle of the oral aperture.
Depressor labi inferioris: extends from the mandible to the lower lip.
Risorius: This extends from the parotid fascia to the angle of the oral aperture. It is a smiling muscle.
Muscles of the Ear
Auricularis anterior: Lies in front of the ear.
Auricularis superior: Lies superior to the ear.
Auricularis posterior: Lies posterior to the ear.
Corrugator supercilii: This extends from the bridge of the nose to the eyebrow.
Procerus: This extends from the bridge of the nose into the skin over glabella.
Mentalis: This extends from the mandible into the skin of the chin.
BLOOD VESSELS (Fig. 10)
Superficial temporal artery: It is the terminal branch of the external carotid artery. It ascends up into the scalp and supplies the temporal area above the zygomatic arch. The transverse facial artery—Locate this artery below and parallel to the zygomatic arch. It is a branch of the superficial temporal artery. It runs parallel to the zygomatic arch and above the parotid duct. It supplies the cheek region.
Facial artery: It is a branch of the external carotid artery. It reaches the face in front of the masseter muscle. It ascends up to the angle of the eye. It is tortuous in its course. This is to accommodate the artery during movements of the mouth. It gives inferior labial artery to supply the lower lip, superior labial artery to supply the upper lip and nasal artery to supply the side of the nose. Trace these arteries. The corresponding veins accompany the artery.
FACIAL NERVE (Fig. 11)
The facial nerve is the 7th cranial nerve and is the motor nerve of this region. It supplies all the muscles of facial expression. Its branches are to be located around the parotid gland. They enter the face deep to the parotid gland. The branches of the nerve appear along the borders of the parotid gland, pass deep to the muscles and supply them on their deeper aspect. The distribution is highly variable. Following gives standard distribution.
Temporal branch: It is seen along the upper border of the parotid gland in front of the superficial temporal artery. This nerve runs parallel with the artery and supplies the auricularis superior, anterior frontal belly of occipitofrontalis and orbicularis oculi.
Zygomatic branch: This runs parallel to the zygomatic arch, supplies the muscles zygomaticus major and zygomaticus minor arising from the zygomatic bone. It runs further to supply the muscles of nose. Trace these branches.
Upper buccal branch: This leaves the parotid gland anteriorly. Trace this nerve. It runs between the transverse facial artery and the parotid duct. Trace it forwards into the muscles of upper lip, i.e. orbicularis oris levator labi superioris and levator anguli oris.
Lower buccal nerve: Trace this nerve from the anterior border of the parotid gland, below and parallel to the parotid duct and supplies the buccinator and risorius muscle.
Mandibular branch: This arises near the lower border of mandible (can be seen in the neck dissection). It enters the deep surface of depressor anguli oris and depressor labi inferioris to supply them. Trace these branches.
Cervical branch: This supplies the platysma and can be seen in neck dissection.
PAROTID GLAND (Fig. 12)
Parotid gland is a salivary gland. It is the biggest of the salivary glands. It is enclosed in the deep fascia of the neck. It is called parotid fascia. Note the irregular shape of the gland. Superiorly it extends up to the zygomatic arch and the external auditory meatus. You have already noted the nerves and blood vessels in relation to the gland.
Parotid duct: Trace this from the middle of the anterior border of the gland. Trace it forward between the upper and lower buccal nerves. Note that it pierces the buccal pad of fat and the buccinator muscle. Its opening in the oral cavity can be seen at a later dissection.
Facial nerve: This is the most superficial of the structures within the gland. Dissect the branches of the nerve into the gland. Its arrangement in the gland is variable. However in general it is seen as two trunks, an upper and a lower. A small part of the gland is clasped between the two divisions. The part superficial is considered as the superficial part. Slowly remove this.
Retromandibular vein: Identify this vein running vertically within the substance of the gland. It is formed by the union of the superficial temporal and the maxillary veins. It divides into an anterior and a posterior division within the substance. Locate these branches.
External carotid artery: Trace this artery in the gap between the posterior border of the mandible and the mastoid processes. Trace the superficial temporal artery and the maxillary artery which are its terminal divisions. The part of the gland that is removed to trace these vessels is the deep part of the gland.
Lymph nodes: Many a lymph nodes were removed during the dissection and these are the parotid lymph nodes.
Trigeminal nerve branches supply the skin of the face. The nerve fibres are very thin, pass through the skull before reaching the skin. Try to locate them as per their position, and it is not essential to trace all the branches.
SENSORY NERVES—BRANCHES OF TRIGEMINAL NERVE (Fig. 13)
Trigeminal nerve is the 5th cranial nerve and is sensory to the skin of the face. It has three divisions—the ophthalmic, maxillary and mandibular. The terminal branches of these divisions reach the face through the foraminae in the skull.
Supratrochlear nerve and supraorbital nerve: These nerves were already identified in the dissection of the scalp. Relocate them and trace supratrochlear nerve through the orbicularis oculi to the trochlea and the supraorbital nerve to the supraorbital notch near the medial aspect of the orbit.
Lacrimal nerve: This is a very small branch piercing the upper eyelid on its lateral aspect.
Infratrochlear nerve: This is a very small branch on the bridge of the nose medial to the medial palpebral ligament.
External nasal nerve: This is a very small branch on the bridge of the nose. It pierces to the surface between the nasal bone and alae of the cartilage.
Zygomaticotemporal nerve: It is a very small branch piercing through the temporal fascia above the zygomatic arch.
Zygomaticofacial nerve: It is a very small branch piercing through the zygomatic bone on the face. Try to see its position on a dry skull.
Infraorbital nerve: This is a thick nerve, reaches the face through the infraorbital foramen. Lift the orbicularis oculi and the levator labi superioris, feel the intraorbital foramen, and locate the thick infraorbital nerve which comes out as a bunch of nerves.
Auriculotemporal nerve: This was already identified in the dissection of the scalp. Relocate the nerve and trace up to the upper border of the parotid gland.
Buccal nerve: This is a deep branch. It passes through buccal pad of fat and buccinator muscle to supply the skin of the cheek. Identify this at this stage so that it can be traced in a later deeper dissection.
Mental nerve: This is a thick nerve and reaches the face through the mental foramen. Lift the depressor labi inferioris to locate this nerve.
Study the neck on a living person and observe the following:
Note that the cervical vertebrae are posteriorly located. The neck extends far higher on the posterior aspect, compared to the anterior aspect. In the midline anteriorly, the trachea and esophagus are located. These are supported by cartilages. The neck can be divided into two parts for convenience of study. The sternocleidomastoid is the key muscle here. It extends from the mastoid process to the sternum and clavicle. It is used to divide the neck into an anterior part, the anterior triangle in front of the sternocleidomastoid and a posterior part, the posterior triangle behind the sternocleidomastoid.
The posterior triangle is made up of vertebral musculature. It is narrow superiorly, but widens inferiorly and spans from the vertebral processes to the scapula, clavicle and the upper ribs. It presents a layered appearance. The most superficial group belongs to the upper limb, the middle group belongs to the erector spinae group of musculature. The deep group belongs to the rotator group of vertebral musculature.
The anterior triangle is made up of visceral structures. In its upper part it is the pharynx, the common passage of both respiratory and digestive system. Inferiorly it divides into trachea and esophagus. The thyroid and parathyroids form the prominent structures ventral to the trachea.
The neurovascular bundle lies between the two. The veins of the neck called the jugular system of veins form a superficial group and a deep group. Branches of the arch of the aorta enter the neck as brachiocephalic artery on the right side and as common carotid artery and the subclavian artery on the left side. They supply the upper limb, head and neck and the brain. The lymph nodes accompany the veins by forming a superficial and a deep group.
9th, 10th, 11th and 12th cranial nerves show their presence in the neck region. The somatic nerves form the cervical and brachial plexuses. The sympathetic chain along with three ganglia are noted here.
SKELETON (Fig. 14)
The skeleton of the neck is formed by the cervical vertebrae. Go to an articulated skeleton and identify the vertebrae. Do a detailed study of the individual vertebrae.
Atlas: This is the first cervical vertebra. It articulates with the skull. Identify its anterior arch, anterior tubercle, lateral masses, foramen transversarium, articulating surfaces on the lateral masses, posterior arch, posterior tubercle and the groove for the vertebral artery on the posterior arch.
Axis: This is the second cervical vertebra. It has an odontoid process which is the detached part of the body of the atlas. It resembles other cervical vertebrae except for this process. Identify the body, odontoid process, transverse process, pedicle, lamina and the bifid spine. This articulates superiorly with the atlas by a pivot joint.
Three to seven vertebrae: Identify the general features of these vertebrae. They present a body, pedicle, the transverse process with a foramen transversarium, anterior tubercle, costotransverse bar and a posterior tubercle, lamina and a bifid spine.
SURFACE ANATOMY (Fig. 15)
Most of the following structures were already identified by you. As they form boundaries for this region, they are once again emphasized.
Symphysis menti: It is the lower point of the mandible in the midline.
Lower border of the mandible: Run your fingers from the symphysis menti to the angle of the mandible.
Angle of the mandible: The posteroinferior corner of the mandible at the junction of the body and ramus.
Mastoid process: Put your fingers behind the ear and feel for the downward projection.
Press and identify the gap between the above two points and note the parotid gland in it.
External occipital protuberance and superior nuchal line: Identify these on the skull from the midline to the lower end of the mastoid process and relocate them on the cadaver.
Ligamentum nuchae and cervical spines: Run your fingers along the midline posteriorly till you reach the 7th cervical vertebral prominence.
Acromion process: Lies under the shoulder prominence, feel this by pressing through the deltoid muscle.
Clavicle: It is subcutaneous throughout its length and can be felt all along.
Suprasternal notch: This lies at the upper border of the manubrium sterni between the two clavicles.
Hyoid bone: Run your fingers downward from the symphysis menti along the midline and clasp the bone between your two fingers. You move it by holding the greater cornu of the bone.
Thyroid cartilage: This causes a prominence more pronounced in male members called Adam's apple. Again clasp it between your fingers.
Cricoid cartilage and tracheal rings: These can be felt in the midline below the thyroid.
Supraclavicular fossa: This is a depression above the middle of the clavicle and posterior to the sternocleidomastoid muscle.
Sternocleidomastoid muscle: Turn the head to one side and identify the muscle which stands out extending from manubrium sterni to mastoid process.
External jugular vein: Identify this vein, on a well developed body.
External carotid artery: Feel the hyoid bone, and press your fingers in, to feel the carotid artery.
Posterior triangle is the area between the sternocleidomastoid and trapezius extending from the middle of the clavicle to the superior nuchal line. It is a narrow long strip of triangle. This can be divided into two subtriangles by the inferior belly of omohyoid muscle. The upper part is called the occipital triangle and the lower part is called the subclavian triangle.
Anterior border is formed by the posterior border of sternocleidomastoid muscle; posterior border is formed by the anterior border of the trapezius muscle; roof is formed by the skin, superficial fascia with cutaneous vessels and nerves and platysma muscle; floor is formed by the prevertebral muscles—the semispinalis capitis, splenius capitis, levator scapulae and scalenus medius. Number of structures cross this area to reach their destination in the present study follow the structures as they appear in the dissection.
Platysma muscle (Fig. 16): It is a thin subcutaneous muscle stretching over the sternocleidomastoid to the clavicle. It helps in tightening the neck skin. It is supplied by the cervical branch of the facial nerve.
CUTANEOUS STRUCTURES (Fig. 17)
External jugular vein: Locate this vein on the sternocleidomastoid muscle and trace it till it pierces through the deep fascia, posterior to the sternocleidomastoid muscle. It receives suprascapular and transverse cervical veins.
Cutaneous nerves: Trace the nerves along the posterior border of the sternocleidomastoid muscle. Note that the supraclavicular nerves descend down toward the clavicle, the lesser occipital nerve towards the scalp. The great auricular nerve crosses on to the sternocleidomastoid muscle to reach the external ear. The transverse cervical nerve runs across the sternocleidomastoid muscle.
The accessory nerve, (XIth cranial nerve) passes between the two layers of the investing layer of the cervical fascia. It loops with the lesser occipital nerve. This helps in identifying this nerve. You need to clean the fascia to locate this nerve.
DEEP FASCIA—INVESTING LAYER OF CERVICAL FASCIA
The trapezius and sternocleidomastoid belong to the superficial group of musculature. Both these muscles are enclosed in the investing layer of cervical fascia. The fascia extends from the ligamentum nuchae, encloses the trapezius, then the two layers unite along its anterior border to form the roof of the posterior triangle, encloses the sternocleidomastoid muscle covers the structures of the anterior triangle to be continuous with the fascia of the opposite side.
Sternocleidomastoid: It is the key muscle in the neck region. It has a clavicular head and a sternal head. Look for the origin of the clavicular head from the superior border and anterior surface of the medial 1/3 of the clavicle. Here it has a muscular origin. The sternal head arises from the anterior surface of the manubrium sternum. Both the origins soon join to form a thick muscle mass, which extends posteriorly to be inserted. Locate its insertion into the mastoid process along a curved line.
Action: Look at this muscle extending from the front to the back of the neck. It pulls the mastoid processes downwards, thus results in lifting the face upwards. When muscle of one side acts it will pull the mastoid forwards thus turning the face to the opposite side.
BACK OF THE NECK Skin incisions (Fig. 18)
SUPERFICIAL FASCIA and CUTANEOUS STRUCTURES (Fig. 19)
Superficial fascia and cutaneous structures: Here superficial fascia has lot of connective tissue, so feels tough, and it is filled with fine fat.
Greater occipital nerve: This nerve is already identified in the scalp region, trace it down, between the trapezius and sternocleidomastoid. Note the occipital artery accompanying this.
Third occipital nerve (C3): This nerve pierces lateral to the 3rd cervical spine. If possible locate this. The other posterior cutaneous nerves from 4th to 8th also pierce in their respective positions lateral to the midline to supply the skin on the posterior aspect. They are small and do not bother to trace all of them.
Lesser occipital nerve: Trace this nerve along the posterior border of the sternocleidomastoid muscle.
Trapezius: This is a muscle of the upper limb. It attaches the upper limb to the trunk bones.
Origin: It extends from the external occipital protuberance to the last thoracic spine in the midline, (the thoracic part has already been dissected) and from the medial 1/3 of the superior nuchal line. Trace this part now.
Now identify the muscles that lie deep to the trapezius. They form the posterolateral group of musculature. They constitute two groups—The erector spinae (extensors of spine) group and the lateral rotator group.
The occipital artery and the posterior rami of the cervical nerves supply this musculature. Try to see as much as you can. Try to reflect the muscles layer by layer.
Occipital artery: It is the artery of supply to this region. It gives off a superficial and a deep branch, which goes between the muscles to supply them. Trace these branches as you are reflecting the muscles.
Motor nerves: The posterior rami of the upper cervical nerves give branches to supply the muscles of the back.
Splenius capitis (Fig. 21): Identify this muscle from the direction of its fibres. They extend from the midline to the lateral side.
Trace its origin from the lower part of the ligamentum nuchae and the upper six thoracic vertebral spines. Note its insertion into the superior nuchal line and mastoid process, deep to the sternocleidomastoid muscle.
See the deeper splenius cervices muscle. Its origin is same as the capitis but few of these fibres get inserted into the transverse process of the upper four cervical vertebrae. This is called the splenius cervices.
Semispinalis capitis (Fig. 22): This muscle fibres run opposite to the splenius capitis muscle. This muscle extends from lateral to medial side. It arises from the transverse process of upper six thoracic and lower four cervical vertebrae and is inserted into the medial aspect of the area between the superior and inferior nuchal lines.
Longissimus capitis: Identify this muscle under cover of the splenius capitis. It extends from the upper thoracic transverse processes to be inserted into the mastoid process. Detach this muscle from the mastoid process to get a clearer view of the suboccipital triangle. The fibres which get inserted into the posterior aspect of the cervical transverse processes is called the longissimus cervicis muscle. You may identify these fibres.
Action of all the above muscles belonging to the superficial group of erector spine group of muscles perform extension of the cervical part of vertebral column.
Ligamentum nuchae: Identify this midline thick ligament extending from the external occipital protuberance to the 7th cervical vertebra. This is a thick ligament made up of elastic fibres. With reflexion of the posterior muscles this ligament becomes visible. Appreciate its thickness and length.
The following muscles were cut in the upper limb dissection. Trace them to their origins. They are lateral rotators of the vertebral column.
Levator scapulae (Fig. 23): Note this lateral muscle. This arises from the transverse processes of the upper four cervical vertebrae. It is inserted into the medial border of the scapula above the spine (as the upper limb is already detached, note its lower cut end and confirm its insertion on scapula).
Scalenus medius: It is another lateral muscle. It arises from the posterior tubercles of the transverse processes of cervical vertebrae. It is inserted into the external surface on the middle of the first rib (confirm its insertion as a part of the first rib is still present with the trunk).
Inferior belly of omohyoid: It is an obliquely running muscle. It arises from the upper border of the scapula medial to the suprascapular notch (as the upper limb is detached it is cut but confirm it on the bone). It is inserted into the intermediate tendon which is under cover of the sternocleidomastoid (This will be studied in the anterior triangle).
The blood vessels and nerves forming the contents can be better traced in a later dissection.
SUBOCCIPITAL TRIANGLE (Fig. 24)
Suboccipital triangle is a muscular triangle made up of deep layer of erector spinae group of musculature.
The roof is formed of skin, superficial fascia, trapezius muscle, splenius capitis and semispinalis capitis muscle. These are the muscles you had already seen and reflected.
The medial boundary is formed by two muscles.
Identify the bigger lateral muscle, the rectus capitis posterior major. It partly overlaps the medial rectus capitis posterior minor muscle. It arises from the spine of the axis and gets inserted into the area between the inferior nuchal line and the foramen magnum lateral to the rectus capitis posterior minor.
Rectus capitis posterior minor: This is a small muscle on the medial side. It arises from the posterior tubercle of atlas and gets inserted into the area between the inferior nuchal line and foramen magnum.
Identify the superolateral boundary. It is formed by the obliquus capitis superior. It arises from the transverse process of atlas and is inserted into the area between the superior nuchal line and inferior nuchal line lateral to the insertion of semispinalis muscle.
Identify the obliquus capitis inferior. This forms the inferior boundary. It arises from the spine of the axis and gets inserted into the transverse process of the axis.
Nerve supply of all the above muscles are supplied by the C1 posterior ramus—the suboccipital nerve.
Action: All the above muscles are rotators of the axis at the atlantoaxial joint. It is a pivot joint (see the bones, articulate them and perform the movements. Here the axis is the fixed part over which the atlas and the occiput rotates).
SUBOCCIPITAL TRIANGLE—LOOR (Fig. 25)
Greater occipital nerve: Relocate this nerve and note that it emerges below the obliquus capitis inferior, pierces the semispinalis capitis to reach the scalp.
Suboccipital nerve: It is seen immediately above the posterior arch of atlas between it and the vertebral artery. It communicates with the greater occipital nerve and supplies all the suboccipital muscles.
Identify the structures forming the floor of the suboccipital triangle.
Feel the prominent posterior arch of atlas. It is the bony prominence extending from right to left.
Vertebral artery: Identify this soft bulging artery extending from the foramen transversarium of the atlas to the foramen magnum.
Posterior atlanto-occipital membrane: Locate this medial to the vertebral artery. It extends from the posterior arch of atlas to the margin of the foramen magnum. Feel it, it is a resilient structure.
This is the area in front of the sternocleidomastoid to the midline. It extends superiorly from the mastoid process to the angle of the mandible, along the lower border of the mandible to the symphysis menti. Inferiorly it extends from the medial ends of the clavicle and the upper border of the manubrium sternum.
INCISION LINES (Fig. 26)
PLATYSMA (Fig. 27): This is the subcutaneous muscle of the neck. It extends downwards and laterally from the lower border of the mandible, crosses over the clavicle to be inserted into the skin.
Cervical branch of facial nerve: Look for this nerve on the undersurface of the muscle. It enters the muscle behind the angle of the mandible at the lower border of the parotid gland.
Identify the following structures in the midline.
The symphysis menti, median raphae, thyrohyoid membrane, anterior angle of thyroid cartilage (Adam's apple) cricotracheal membrane and upper tracheal rings.
CUTANEOUS STRUCTURES (Fig. 28)
External jugular vein: This was already identified at its lower end. Trace it up to its formation. It is formed by the union of posterior auricular vein and the posterior branch of the retromandibular vein. This is one of the superficial veins which can be easily accessed in the body.
Anterior jugular vein: Identify this thin vein lateral to the midline. It begins below and near the symphysis menti, runs down crosses laterally to enter into the external jugular vein.
Great auricular nerve: Trace this nerve from the middle of the sternocleidomastoid to the ear lobule along the superficial surface of the sternocleidomastoid. It is a part of the cervical plexus and supplies the skin up to the angle of the mandible.
Transverse cervical nerve: Trace it from the middle of the sternocleidomastoid to the midline across the muscle.
Supraclavicular nerves: Trace these nerves from middle of the posterior border of the sternocleidomastoid to over the clavicle. They are generally three in numberthe medial, intermediate and lateral branches. (These were already cut).
ANTERIOR TRIANGLE—SUBDIVISIONS (Fig. 29)
The anterior triangle is the triangular area from the anterior border of the sternocleidomastoid, the lower border of the mandible and the midline. In this area, identify the anterior belly of digastric, posterior belly of digastric and the superior belly of omohyoid. These muscles are used to divide the anterior triangle into four smaller triangles for convenience of description. Study them.
- Submental triangle: This is a midline triangle. Identify the body of the hyoid bone. This forms its base. Look for the anterior bellies of the digastric muscles. These form the limbs of the triangle.
- Submandibular triangle/digastric triangle: Feel the lower border of the mandible. This forms the base of this triangle. Identify the anterior and posterior bellies of the digastric muscle. They form the sides of the triangle. See the prominent submandibular gland in this region.
- Muscular triangle: Look at the muscles on either side of the midline below the hyoid bone. It is made up of two layers. The superficial layer is split vertically. The medial muscle is sternohyoid, and the lateral muscle is the superior belly of omohyoid (the deeper muscles can be seen in a later dissection).
- Carotid triangle: It is the lateral triangle. The base is formed by the anterior border of the sternocleidomastoid muscle. The limbs are formed by the posterior belly of digastric and superior belly of omohyoid. The neurovascular bundle of neck is located here.
STERNOCLAVICULAR JOINT—DISARTICULATION (Fig. 30)
Subclavius muscle: This was already studied while doing the upper limb dissection. Restudy this muscle. It arises from the 1st rib and costal cartilage, moves upward and laterally to be inserted into the undersurface of the clavicle in the subclavian groove.
It is a joint of the pectoral girdle attaching it to the trunk skeleton. It is a plane synovial joint. The medial surface of the clavicle articulates with the upper facet on the manubrium sternum. It is covered by capsule on all sides and is thicker anteriorly.
Costoclavicular ligament: Locate this ligament on the undersurface of the medial end of the clavicle and the upper surface of the 1st costal cartilage.
INLET OF THORAX (Fig. 31)
The inlet of thorax is formed by the 1st thoracic vertebra, the 1st rib and the upper border of manubrium sternum. The rib is obliquely placed. The upper border of the manubrium lies at the level of the lower border of the 2nd thoracic vertebra. The inlet is closed on either side by the suprapleural membrane covering the lung and pleura. The trachea, esophagus and the neurovascular bundle passes in the midline between the two lungs. Due to the obliquity of the 1st rib all the structures passing between the thorax and the neck are exposed above the 1st rib, but they are covered by the positioning of the clavicle and subclavius muscle. The gap between the scapula, outer border of first rib and the clavicle is the apex of the axilla through which the neurovascular bundle reaches the upper limb (See the bony parts on a skeleton).
Suprapleural membrane/Sibson's fascia/scalenus minimus: This is the fascia covering the pleura. Locate its extent. This is the scalenus minimus muscle which is totally replaced by membrane. It arises from the tip of the transverse process of the 7th cervical vertebra and is inserted into the inner border of the first rib. Feel this from both thorax side and neck side. Clear this fascia to see the continuity of the structures from the thorax.
STUDY OF MUSCLES (Fig. 32)
Here the muscles are arranged in two layers—a superficial sternohyoid and omohyoid and a deeper sternothyroid and thyrohyoid muscles.
Omohyoid muscle: It arises from the body and the greater horn of the hyoid bone. Note a thick sling of connective tissue that connects the intermediate tendon to the back of the clavicle. Lift up this muscle and look for the nerve supplying the bellies on their undersurface. They are supplied by branches of the ansa cervicalis.
Sternohyoid: Note this muscle medial to the omohyoid. It arises from the back of the manubrium sternum and is inserted into the lower border of the body of the hyoid. Trace the nerve of supply from the ansa cervicalis into this muscle.
Sternothyroid: Identify this muscle which lies deep to the sternohyoid muscle. It arises from the back of the manubrium sternum, below the origin of the sternohyoid. It is inserted into the oblique line of thyroid cartilage. It is supplied by a branch of the ansa cervicalis.
Actions: All the strap muscles depress the larynx.
It is a nerve loop over the surfaces of the carotid sheath. Its loop supplies the strap muscles—omohyoid both the bellies, sternohyoid and sternothyroid muscles.
Superior root of ansa cervicalis: Trace this limb between the internal jugular vein and the common carotid artery. Trace it superiorly and note that it is a branch of the hypoglossal nerve.
Inferior root of ansa cervicalis: Look for two branches winding round the internal jugular vein joining together and joining the superior root of ansa.
Ansa cercivalis is a part of the cervical plexus. It is contributed by C1, 2 and 3 ventral rami. The C1 fibres reach ansa through hypoglossal nerve and the C2 and 3 fibres wind round the internal jugular vein.
The loop formation is variable in its position. Branches to the strap muscles are given off from the loop.
Thyrohyoid muscle: This is also one among the muscles of muscular triangle. It arises from the oblique line on the thyroid cartilage and is inserted into the lower border of the greater cornu of the hyoid bone. It is supplied by C1 fibres through a branch of the hypoglossal nerve. It is an elevator of larynx. Trace the nerve into the muscle.
Lobes: Locate them on the sides. They are conical in shape. The upper pointed end extends up to the oblique line of thyroid cartilage. Inferiorly it is broader and extends up to the inlet of thorax. Each lobe presents a medial surface, anterior surface and a posterior surface.
Note: That the medial surface is related to the trachea and esophagus at its lower part, larynx and pharynx at its upper part. The posterior surface is related to carotid sheath. Anterior surface is overlapped by the strap muscles.
The isthmus lies over the 2, 3, and 4th tracheal rings. Levator glandulae thyroid is a small strip of the glandular tissue extends from the left side of the upper border of the isthmus to the hyoid bone. It is variable in size.
Identify the superior thyroid artery at the upper pole of the gland. The superior thyroid artery divides into anterior and posterior branches, trace them as for as possible. The superior thyroid artery is accompanied by external laryngeal nerve. Trace it to the cricothyroid muscle. The inferior thyroid artery enters the lower pole of the thyroid. It arises from the 1st part of the subclavian artery. This branch supplies the inferior part of the thyroid gland. The thyroidea ima artery is a branch of the aorta and enters the lower border of the isthmus.
Veins: Generally there are three veins draining the thyroid lobes. The superior and middle thyroid veins drain into the internal jugular vein and the inferior thyroid vein drains the isthmus into the brachiocephalic vein. The lymphatic drainage accompanies the veins. Trace the recurrent laryngeal nerve which accompanies the inferior thyroid artery. The association of the nerve to the artery is to be taken care of during thyroid surgeries.
Parathyroid glands: Clean the connective capsule and locate the parathyroid glands. The superior parathyroid lies in the middle of the gland. The inferior parathyroid gland lies nearer to the inferior pole of the thyroid.
The subclavian artery, its branches, the common carotid artery, the internal carotid artery, the external carotid artery and its branches form the arterial system in the neck. The anterior, external and internal jugular veins with their tributaries form the venous system. The 9th, 10th, 11th and 12th cranial nerves, the cervical and brachial plexus and the sympathetic chain form the nerves of the neck. Superficial and deep lymph nodes accompany these veins. The brachiocephalic trunk divides into common carotid artery and the subclavian artery on the right side whereas the common carotid and subclavian arteries arise independently from the arch of the aorta on the left side. Locate and trace these vessels from the thorax.
Carotid sheath: It is the thick fascial sheath which encloses the neurovascular bundle from the upper thorax to the base of the skull. It encloses the internal jugular vein and vagus nerve throughout its extent, the common carotid artery in the lower part and internal carotid artery in its upper part. It encloses the glossopharyngeal and the accessory nerve along with the vagus nerve in its upper part.
VEINS (Fig. 35)
Identify the major veins, the external jugular, subclavian, internal jugular and the brachiocephalic veins; if possible locate its tributaries.
External jugular vein: It lies superficial to the sternocleidomastoid and receives veins of the posterior region—the transverse cervical and the dorsal scapular. It receives the anterior jugular vein from the anterior aspect (already identified).
The subclavian vein: It extends from the outer border of the 1st rib to the inner aspect of the sternoclavicular joint, where it joins with the internal jugular vein to form the brachiocephalic vein. It receives external jugular veins.
Brachiocephalic vein: This descends down from the sternoclavicular joint to the 1st rib. It receives the veins accompanying the branch of the subclavian artery. It receives vertebral, inferior thyroid, internal thoracic and superior intercostals veins.
Thoracic duct: Locate this lymphatic duct on the left side. It is in front of the 7th cervical vertebra, crosses the subclavian artery and suprapleural membrane to reach the left brachiocephalic vein and empties into it (the thoracic duct the big lymphatic channel has already been identified in the thorax). Trace it up, to its termination.
Right lymphatic duct is a smaller channel. It opens into the right brachiocephalic vein near its formation.
Internal jugular vein: Identify this vein by cleaning the connective tissue of the carotid sheath. It enters the neck at the level of the jugular foramen. It descends down parallel to the carotid arteries. Try to locate its tributaries—the common facial vein, lingual vein, superior thyroid vein, the middle thyroid vein, the subclavian vein and the anterior jugular vein. Except the anterior jugular vein all the other veins accompany the corresponding arteries.
The area between the middle 1/3rd of clavicle, inferior belly of omohyoid and posterior border of sternocleidomastoid muscle is the subclavian triangle. This lodges the subclavian vessels, brachial plexus and other nerves.
SUBCLAVIAN ARTERY (Fig. 36)
The subclavian artery is the artery of the upper limb. It leaves the thorax, crosses over the root of the neck to reach the axilla of the upper limb at the outer border of first rib. Trace the subclavian artery. Note its relation to the scalenus anterior muscle. Conventionally it is divided into three parts1st part from the sternoclavicular joint to the medial border of the scalenus anterior, the second part—behind the scalenus anterior and the third part between the lateral border of the scalenus anterior to the outer border of 1st rib.
Vertebral artery: It is the first branch of the subclavian artery, arises from the anterior aspect, near the transverse process of the 7th cervical vertebra, lies between the scalenus anterior and longus colli and enters the foramen transversarium of the 6th cervical vertebrae.
Thyrocervical trunk: It is the lateral branch from the superior aspect of the subclavian artery. It generally gives off three branches. The inferior thyroid artery turns medially to enter into the posteroinferior aspect of the thyroid gland. The transverse cervical artery—trace this artery across the scalenus anterior and the levator scapulae, there it divides into two branches, the superficial branch enters the deep aspect of the trapezius along with the accessory nerve and the deeper branch goes deeper to levator scapulae and rhomboidei along the medial border of the scapula. These branches were already studied in the dissection of the upper limb.
Internal thoracic artery: It arises from the inferior aspect of the subclavian artery crosses the suprapleural membrane reaches the posterior aspect of the sternoclavicular joint (its thoracic part was already dissected in thoracic).
From the second part of the subclavian artery: Locate this artery by pulling the artery forwards and look for its branches. The superior intercostal artery runs down close to the first two ribs and gives off branches into the intercostals spaces. The deep cervical artery ascends up in front of the scalenus anterior and transverse process of cervical vertebrae and gives off number of muscular branches.
The third part of the subclavian artery does not have any branches.
CAROTID ARTERIES (Fig. 37)
Common carotid artery: On the right side it is a branch of the brachiocephalic trunk, on the left side it is a branch directly from the arch of the aorta. Trace it down to its origin.
Carotid sinus: This is the enlarged upper end of the common carotid artery near its division. At this point the artery has got specialized nerve endings which act as baroreceptors.
Internal carotid artery: This is the artery which supplies brain. It ascends up to the carotid canal in the skull without giving any branche in the neck. It lies parallel and posterior to the external carotid artery. It lies within the carotid sheath throughout its extent.
External carotid artery: It is the artery of the neck and face. It gives off number of branches to supply these regions. Identify the following branches of the external carotid artery.
Superior thyroid artery: This is the first artery from the anterior surface of the external carotid artery above the level of superior horn of thyroid cartilage. Trace its branchesthe infrahyoid branch which runs along the lower border of hyoid bone; the superior laryngeal artery which pierces the thyrohyoid membrane, the muscular branches to sternocleidomastoid and cricothyroid muscle; anterior and posterior thyroid branches near the apex of the thyroid gland.
Lingual artery: It is the next branch from the anterior aspect of the external carotid. It is given off at the level of the greater cornua of hyoid. It presents a looped appearance and disappears under cover of mylohyoid muscle. The branches of the artery can be seen at a later dissection.
Facial artery: Locate this artery immediately above the lingual artery. Trace this artery to the angle of mandible. There it gives off ascending palatine, tonsillar, glandular branches to submandibular gland and submental branch which accompanies the mylohyoid nerve to supply anterior belly of digastric and mylohyoid muscle. Try to see these branches. Beyond this the artery is already traced in the face.
Occipital artery: Note this branch which is given off from the posterior aspect of the external carotid artery near the greater cornua of hyoid, opposite to the facial artery. Trace this artery to the mastoid process along the lower border of posterior belly of digastric muscle, and into the suboccipital triangle where it is already studied. It gives off muscular branches to sternocleidomastoid muscle, and meningeal branch to pass through the jugular foramen.
Posterior auricular artery: This is another artery given off from the posterior aspect. This runs towards the back of the ear along the upper border of the posterior belly of digastric muscle.
Ascending pharyngeal artery: Pull the external carotid artery laterally and look for a small branch of this artery, the ascending pharyngeal artery. It supplies the muscles of pharynx.
Superficial temporal and the maxillary arteries are the terminal branches of the external carotid and are seen in face dissection.
CRANIAL NERVES (Fig. 38)
9th, 10th, 11th and 12th cranial nerves, and all the cervical nerves forming the cervical and brachial plexus and sympathetic chain are located in the neck region. The cranial nerves are located in the carotid sheath along with the blood vessels.
The spinal nerves lie between the scalenus anterior and scalenus medius muscles. The sympathetic chain lies in front of the transverse processes of the vertebrae. Try to locate them.
Hypoglossal nerve: It is the 12th cranial nerve. Locate this nerve between the internal jugular vein and internal carotid artery and inferior to the occipital artery. Trace it across the external carotid artery and crossing the lingual artery to enter deep to the mylohyoid muscle.
Accessory nerve: The 11th cranial nerve lies posterior and lateral to internal jugular vein. It enters the sternocleidomastoid near the posterior belly of digastric.
Vagus nerve: It is the 10th cranial nerve. Identify it in the interval between the internal jugular vein, internal and common carotid arteries. Trace it down into the thorax.
Superior laryngeal nerve is a branch of the vagus nerve. Locate this nerve deep to the carotid artery, trace it forwards. It accompanies the superior thyroid artery. The superior laryngeal nerve gives off the internal and external laryngeal nerves. Trace the internal laryngeal nerve along with the laryngeal branch of superior thyroid artery to the thyrohyoid membrane, the external laryngeal nerve runs down to supply the cricothyroid muscle.
Glossopharyngeal nerve: It is the 9th cranial nerve and will be seen at a later dissection.
SYMPATHETIC CHAIN AND SPINAL NERVES (Fig. 39)
Sympathetic trunk: Pull the carotid vessels medially with a hook and see the sympathetic chain in front of the transverse processes of the cervical vertebrae. Trace its total length. Look for the superior cervical ganglion in front of the 2nd and 3rd cervical vertebrae, the middle cervical ganglion near the 5th cervical vertebra and the inferior cervical ganglion near the neck of the first rib.
The inferior cervical ganglion joins with the 1st thoracic nerve to form the stellate ganglion.
Ansa subclavia: Trace this loop between the middle and inferior cervical ganglia in front of the subclavian artery on the right side.
Gray rami communicantes: These connect the superior cervical ganglion to upper 4 cervical nerves, middle cervical ganglion to 5th and 6th cervical nerves and the inferior cervical ganglion to 7th, 8th cervical nerves, trace as many as possible.
Visceral branches are given off to pharynx, esophagus and heart. These are medial branches, trace as many as possible.
Vascular branches: These accompany the blood vessels, trace as many as you can.
Cervical ventral rami: Trace all the cervical nerves emerging between the vertebrae. They lie on the scalenus medius muscle.
All the cutaneous nerves, the great auricular, lesser occipital transverse cervical supraclavicular were already traced. Trace them to their origin from the cervical nerves and also trace the inferior root of ansa cervicalis to the C2, 3 roots.
Muscular branches: Trace these branches entering into the sternocleidomastoid, levator scapulae, scalenus anterior medius and posterior.
Brachial plexus: Trace the cervical 5,6,7,8 and T1 roots. Note that 5 and 6 join to form upper trunk, 7 forms middle trunk and C8, T1 form lower trunk. Trace these to the first rib. Note that the lower trunk lies deeper to the subclavian artery.
Long thoracic nerve/nerve to serratus anterior, dorsal scapular nerve/nerve to rhomboids, phrenic nerve to diaphragm—trace these nerves to the roots of brachial plexus.
Suprascapular nerve is given off from the upper trunk. It crosses in front of the scalenus medius deep to the omohyoid. It supplies the muscles on the posterior aspect of scapula.
Nerve to subclavius: It arises from the upper trunk. Trace it down across the subclavian artery to reach the upper surface of the subclavius muscle.
Phrenic nerve: Note this nerve on the anterior surface of the scalenus anterior muscle and trace it into thorax. This nerve supplies diaphragm and it has already been traced.
VERTEBRAL TRIANGLE (Fig. 40)
It is the area between the longus colli, 1st rib and scalenus anterior muscle.
Stellate ganglion: It is the inferior sympathetic ganglion. Identify this in front of the neck of the first rib. Note the ansa subclavian arising from here to connect this with the middle cervical sympathetic ganglion.
Vertebral artery: See this arising from the superior aspect of the first part of the vertebral artery. Trace it into the 6th foramen transversarium.
First thoracic nerve: Trace this nerve to join the 8th cervical nerve to form the lower trunk of the brachial plexus.
Recurrent laryngeal nerve: Trace this nerve from the vagus and looping around the subclavian artery on the right side. On the left side it is given at a much higher level. Trace this nerve into the groove between the trachea and esophagus.
MUSCULATURE (Fig. 41)
Scalenus anterior muscle: Clean the scalenus anterior muscle. It arises from the transverse processes of 3rd to 6th cervical vertebrae. The three heads join together and descend down to reach the scalene tubercle on the inner border of the 1st rib. The muscle separates subclavian vein from the subclavian artery. Remove this muscle totally preserving the phrenic nerve. This muscle is already detached, trace it to its origin.
Scalenus medius: This muscle lies posterior to the brachial plexus. It arises from the posterior tubercles of the transverse processes of 2nd to 6th cervical vestebrae. The fibres join together to insert into the superior surface of the first rib, posterior to the groove for the subclavian artery.
Scalenus posterior: This is a small muscle arising from the 3rd to 6th posterior tubercles of the transverse processes and is inserted into the external surface of the middle of the second rib.
Ventral musculature: Try to identify the following musculature, after studying all the viscera.
Longus colli: It is the muscle on the ventral aspect of the vertebral column. Push the viscera medially and try to locate the muscle. It extends from the transverse processes to the bodies of the cervical vertebra and upper three thoracic vertebrae. Superiorly it reaches the anterior tubercle of atlas.
Action: All these muscles are flexors of the cervical vertebrae.
Rectus capitis anterior: This is a ventral muscle. Try to see this in a dissected specimen. It extends from the lateral mass of atlas, to the base of the skull in front of condyles. It is a flexor of the occiput.
Rectus capitis lateralis: It is an anterolateral muscle. It arises from the superior surface of the transverse process of atlas and gets inserted into the jugular process of the occipital bone. It is a lateral rotator. It is supplied by the ventral ramus of first cervical nerve. Trace this nerve between the above two muscle. It supplies both the muscles.
DIGASTRIC TRIANGLE (Fig. 42)
Stylohyoid muscle: Note this superficial muscle. It arises from the styloid process, lies superficial to the posterior belly of digastric, clasps the intermediate tendon of digastric to the hyoid bone. It is supplied by the facial nerve.
Digastric muscle: It has got two bellies, it extends from mastoid process to the chin. Note the posterior belly near the angle of the mandible and trace it to its origin. It arises from a groove medial to the mastoid process. Note the anterior belly near the chin. It arises from the fossa on the undersurface of the mandible. Trace it down towards the insertion. The muscle is inserted by means of an intermediate tendon which is anchored to the greater cornu of hyoid bone by the stylohyoid tendon.
The above muscles are elevators of the hyoid bone. They help in deglutition.
SUBMANDIBULAR GLAND (Fig. 43)
Submandibular gland: It is one of the salivary glands. What is seen between the two bellies of the digastric muscle is the superficial part of the gland. Note that it is occupying the space between the mandible laterally and the mylohyoid muscle medially. Note the submandibular fossa on a mandible, which is caused by this gland.
Mylohyoid muscle: Identify this muscle lying deep to the submandibular salivary gland and extending up to the midline. The mylohyoid muscle arises from the mylohyoid line on the inner aspect of the body of the mandible and is inserted into the upper border of body of the hyoid bone. In the midline it joins with the muscle of the opposite side and forms a raphae. It is supplied by the mylohyoid branch of the mandibular nerve. Press the muscle and look for the nerve entering into the lateral surface of the muscle. This supplies the anterior belly of digastric also. See both the branches. It is an elevator of larynx.
Look for the free posterior border of this muscle and identify the hypoglossal nerve and the deep part of the submandibular gland and its duct disappearing behind this border.
Hyoglossus muscle: Identify this muscle lying posterior and deeper to the mylohyoid muscle. The hyoglossus muscle arises from the greater cornua of the hyoid bone. The insertion of this muscle will be seen in the tongue dissection.
Lingual artery: Note this artery passing deep to the hyoglossus muscle.
DEEP DISSECTION OF HEAD
TEMPORAL AND INFRATEMPORAL REGIONS
The temporal fossa is the area over the squamous part of the temporal bone. Superiorly it is limited by the superior temporal lines. Inferiorly the temporal fossa is continuous with the infratemporal fossa.
The infratemporal fossa is the area between the pterygoid plates, base of the skull and the mandible (Identify these on the skull).
Temporal and infratemporal region are occupied by muscles of mastication. The temporomandibular joint lies surrounded by its muscles. The neurovascular bundle to supply this region is mandibular nerve and second part of maxillary artery.
Masseter muscle (Fig. 44): It is a thick muscle on the lateral aspect of the ramus of the mandible. It arises from the inferior margin and deep surface of the zygomatic arch. It is inserted into the lateral surface of the ramus. Note the direction of its fibres, they run downwards and posteriorly.
Action: It elevates, protracts and helps in side-to-side movement.
Temporal fascia: Study this thick fascia over the temporal fossa. It is attached to the superior temporal line (locate it on the skull) above and the upper border of the zygomatic arch below. Note that while removing the masseter this margin is cut, and the temporalis below this level is devoid of the fascia. The temporal fascia gives attachment to the temporalis muscle on its deeper aspect.
Temporalis muscle (Fig. 45): It is a fan-shaped muscle occupying the temporal fossa. The muscle arises from the temporal fossa up to the inferior temporal line and from the temporal fascia. Note its insertion into the coronoid process, along its anterior border and inner surface. Note the direction of the fibres. The posterior fibres traverse horizontally and the anterior fibres traverse vertically. The muscle is a retractor and an elevator.
Stylomandibular ligament: Locate the styloid process and trace this ligament to the angle of the mandible. It is the deep part of the parotid fascia, acts as a sling to suspend mandible.
INFRATEMPORAL REGION—SUPERFICIAL DISSECTION (Fig. 46)
Maxillary artery second part: It is a superficial structure seen in here. It generally runs across the lateral pterygoid, or it goes deep, either below the inferior head or between the two heads of lateral pterygoid muscle. Locate the muscular branches to masseter, temporalis, pterygoid muscles and the buccal artery, accompanying the buccal branch of mandibular nerve.
The buccal branch of mandibular nerve is a sensory branch to supply the buccal pad of fat and the skin over the cheek. Locate this nerve passing between the two heads of lateral pterygoid to the cheek.
Lateral pterygoid muscle: This muscle occupies the upper part of the fossa. It arises by two heads, the upper head from the inferior surface of the greater wing of sphenoid, the lower head from the outer surface of the lateral pterygoid plate (confirm these parts on skull). The two bellies unite together to be inserted into the pterygoid fossa on the neck of the mandible. Note that its fibres ascend up from below, and run posteriorly from the front. It is a depressor, protractor and also helps in side to side movement. It is supplied by mandibular nerve on its deeper surface.
Medial pterygoid muscle: This occupies the lower area of the infratemporal fossa. It has a superficial and a deep head. The superficial head arises from the maxillary tuberosity and the deep head arises from the medial aspect of the lateral pterygoid plate. These two heads soon unite and get inserted into the medial aspect of the angle and ramus of the mandible (see them on the skull). Note that the fibres run downwards, posteriorly and laterally. It is an elevator, protractor and helps in side to side movement. Nerve supply is given off from the trunk of the mandibular nerve. It enters the infratemporal fossa through the foramen ovale (locate this foramen on the skull). Locate this nerve near the base of the skull.
Mandibular nerve: It is a branch of the trigeminal nerve. It leaves cranial cavity through the foramen ovale. As soon as it enters the infratemporal fossa it gives off three branches from the trunk, and then divides into an anterior division and a posterior division. The trunk gives off the nervus spinous, nerve to medial pterygoid, nerve to tensor tympani. The anterior division is predominantly a motor division except for buccal nerve which is a sensory branch. The posterior division is predominantly sensory nerve except for the motor branch to the mylohyoid muscle and the anterior belly of digastric.
The anterior division gives off the nerve to the masseter, lateral pterygoid, deep temporal nerves. Its sensory branch is the buccal branch. All these nerves are already identified. All of them were seen between the base of the skull and the lateral pterygoid muscle.
The posterior division gives off three branches, the lingual, buccal and the inferior alveolar nerves. Locate the lingual nerve which is a thick nerve and runs from the lower border of the lateral pterygoid muscle, in an anterior direction to reach the side of the tongue. Pull it forwards and locate the chorda tympani nerve joining it on its posterior side. The point of junction with the lingual nerve is variable. The lingual nerve carries general and taste sensations from the anterior 2/3rds of the tongue. Trace the buccal nerve which lies between the two heads of the lateral pterygoid to the buccal pad of fat on the buccinator muscle. Trace the lingual nerve extending from the lower border of the lateral pterygoid to the side of the tongue. Identify the inferior alveolar nerve which lies posterior to the lingual nerve. Trace this nerve to the mandibular foramen (Identify it on a dry mandible). This is the sensory nerve to the lower jaw, its terminal branch mental nerve has already been identified in face. Trace the mylohyoid nerve from the posterior aspect of the inferior alveolar nerve. It is motor to the mylohyoid and anterior belly of the digastric muscles.
TEMPOROMANDIBULAR JOINT (Fig. 47)
This is the only synovial joint of the skull. The head of the mandible articulates with the mandibular fossa and the articular tubercle of the temporal bone. It is covered by fibrous capsule.
Lateral ligament: It extends from the articular tubercle on the zygomatic arch to the lateral aspect of the neck of the mandible.
The articular disc (Fig. 48) is a fibrocartilaginous structure. Look that its superior surface is concavo-convex and its inferior surface is convex.
Movements: Though it is uniaxial type of joint, it performs more movements because of the presence of articular disc. Protraction, retraction, elevation, depression and side to side movements are performed here.
Study the details from a Textbook.
INFRATEMPORAL FOSSA—DEEP DISSECTION (Fig. 49)
First part of the maxillary artery: Trace this artery from the external carotid artery. It is related to the neck of the mandible. It gives off five branchesauricular, anterior tympanic, accessory meningeal are fine branches. The middle meningeal artery is a bigger branch. Trace it up to the foramen spinosum. It is accompanied by the meningeal branch of the mandibular nerve. The inferior alveolar artery is another big branch. It descends down to the mandibular foramen. It enters the foramen along with the inferior alveolar nerve.
Sphenomandibular ligament: This is a thin sheet of connective tissue extending from the spine of the sphenoid (see it on the bone) to the lingula on the mandible.
Auriculotemporal nerve: It is given off from the posterior part of the posterior division of the mandibular nerve very near the skull. It generally splits into two, encloses the middle meningeal artery. It ascends posteriorly behind the neck of the mandible to supply the skin on the lateral aspect of the scalp (this has already been identified).
Otic ganglion is a parasympathetic ganglion connected to the mandibular nerve. Pull the posterior division forwards and locate this tiny ganglion with its spider like connections. It is at a deeper plane between the nerve to medial pterygoid and the tensor veli palatini.
Chorda tympani nerve: Identify this nerve joining the posterior aspect of the lingual nerve. It leaves the skull through the petrotympanic fissure (identify this on the skull) and its point of joining the lingual nerve is variable in position. The chorda tympani nerve is a branch of the facial nerve and it carries the secretomotor fibres to the submandibular and sublingual salivary glands and taste sensations from the anterior two thirds of the tongue.
STYLOID APPARATUS (Fig. 51)
Styloglossus muscle: Trace this muscle forwards and downwards to the area between the hyoglossus and mylohyoid muscle. This is one of the extrinsic muscles of the tongue. It arises from the anterior surface of the styloid process and is inserted into the lateral side of the tongue. It is a retractor of tongue.
Stylohyoid muscle: Trace this muscle from the posterior aspect of the styloid process to the hyoid bone. It arises from the posterior surface of the styloid process and at its insertion it splits into two parts clasps the intermediate tendon of the digastric to the greater cornu of hyoid bone.
It is an elevator of the hyoid bone. It is supplied by the posterior branch of the facial nerve (this muscle was already cut in the digastric triangle dissection).
Stylopharyngeus muscle: This is a muscle on the medial side of the styloid process. It arises from the medial surface of the styloid process and is inserted into the posterior border of the thyroid cartilage. It is another longitudinal muscle of the pharynx. It enters the pharynx between the superior and middle constrictor of pharynx.
Glossopharyngeal nerve: Locate this nerve winding round the stylopharyngeus muscle. This supplies the stylopharyngeus muscle. After it enters into the pharynx it is sensory to pharynx and posterior 1/3rd of tongue.
Stylohyoid ligament: Locate this thin ligament extending from the tip of the styloid process to the lesser cornua of the hyoid bone. It is internal to the stylohyoid muscle.
Facial nerve: Note the cut part of this nerve at stylomastoid foramen.
SUBMANDIBULAR REGION (Fig. 52)
Hyoglossus muscle: It is an extrinsic muscle of the tongue. It arises from the greater horn and body of the hyoid bone. It is inserted into the lateral side of the tongue.
Lingual nerve: Trace this nerve from the mandibular nerve in the intratemporal fossa. It runs across the hyoglossus muscle near its upper border. Trace it forward to the tongue. It is sensory to the anterior 2/3rds of tongue. It carries both general and taste sensations.
Submandibular ganglion: It is one of the parasympathetic ganglia. Note this small ganglion suspended from the lingual nerve by two roots. It receives the preganglionic fibres from the chorda tympani nerve. The fibres after relay in the ganglion supply the submandibular and sublingual salivary glands. See the fine branches arising from the ganglion and entering the deep part of the submandibular gland. The secretomotor fibres to the sublingual gland reach in, through lingual nerve.
Deep part of the submandibular salivary gland: Note this small part deep to the mylohyoid and on the hyoglossus muscle. Trace its thick duct to the undersurface of the tongue near the midline. Observe its opening.
Sublingual salivary gland: Note this gland distal to the hyoglossus muscle on the lateral aspect of the genioglossus muscle.
Hypoglossal nerve: This is the 12th cranial nerve. Trace its origin into the carotid sheath. It runs across the hyoglossus muscle along its lower aspect. Note its communication to the lingual nerve. It is a motor nerve to supply the thyrohyoid (already studied), the styloglossus, hyoglossus, genioglossus, geniohyoid and the intrinsic muscles of tongue.
Lingual Artery (Fig. 53)
Locate this artery opposite to the greater horn of the hyoid bone, arising from the external carotid artery. Locate its first branch, the suprahyoid branch. It passes along the upper border of the hyoid bone. Now detach the hyoglossus muscle from the hyoid bone, lift it up, and trace the lingual artery. Note the two ascending branches. These are the dorsal lingual branches. These branches supply the tongue up to the mucous membrane. Identify the fine branch that supplies the sublingual gland, the sublingual artery. Beyond this the continuation of the artery is called as the deep artery of the tongue.
REMOVAL OF SPINAL CORD
By this time you have dissected all the postvertebral muscles. Confirm once more that the postvertebral muscles are grouped as the erector spinae group of musculature, signifying their action as an extensor of the vertebral column.
It extends from the sacrum to the external occipital protuberance. In the lumbar region it lies between the middle and posterior layers of the thoracolumbar fascia. In the thoracic region it extends from the spines of the vertebrae to the angles of the ribs. In the neck region it is best developed and well separated. It extends between the spines of the vertebrae to the posterior tubercles of the cervical vertebrae. Inferiorly they extend on to the upper two ribs, superiorly they occupy the space between the external occipital protuberance and the superior nuchal line to the foramen magnum (Fig. 54).
Epidural space: It is the area between the vertebral column and the dura mater. It is filled with vertebral plexus of veins. They drain the venous blood from the vertebrae and the spinal cord.
The vertebral plexus of veins are devoid of valves. They communicate with the segmental veins. It is easy for pelvic infections to pass through this route to secondarily infect the vertebrae and brain.
Dura mater (Fig. 55): It is the outermost layer of the meninges. It is a tough sheet. Try to mobilize the spinal cord and see. Note that the spinal nerves leave the vertebral canal through the intervertebral foraminae. They are covered by the meninges. The dura mater extends from the foramen magnum to the second sacral vertebra, beyond that identify the thin filum terminale extending up to the coccyx.
The cranial cavity is occupied by the brain. It is covered by three meninges—the pia mater, the arachnoid mater and the dura mater in that order from inside out. The dura mater is very thick. It is made up of two layers, the endosteal and the meningeal layers. The meningeal layer sends in sheets to separate different parts of the brain. The venous sinuses lie at the point of their separation. All the cranial nerves leave the cranial cavity through the foraminae in the skull.
In this study you remove the brain from the cranial cavity along with the pia and arachnoid mater. While removing the brain you will be cutting the cranial nerves arising from it. You will study the dura mater and the venous sinuses as you try to remove the brain.
Take a wet chalk piece and make a mark from (1) Just below the supraorbital margin anteriorly (2) Along the upper border of the attachment of auricle, (3) To a point below the external occipital protuberance. Cut it with a saw and remove the skull cap making sure that you retain the dura mater in situ. Use hand or edge of the scalpel to ease the dura mater from the skull. In general near the midline there can be erosion of the skull cap by the arachnoid granulations. Take more care in this area.
Dura Mater (Fig. 57)
It is the thick white glistening meninges that is exposed now. Note the prominent middle meningeal artery on the superolateral aspect of the dura mater. This reaches the dura through the foramen spinosum. This is a branch of the first part of the maxillary artery. This is the major artery of supply to the dura mater.
The veins of the cranial cavity present a nonvalvular sinus pattern. The venous sinuses lie between the endosteal and meningeal layer of the dura mater. The superior sagittal sinus, the inferior sagittal sinus and the straight sinus lie in the midline. The sphenoparietal sinus, the cavernous sinus, the intercavernous sinuses, the superior and inferior petrosal sinuses are paired sinuses and lie on either side of the midline.
Superior sagittal sinus: This lies in the midline from the foramen cecum to the level of external occipital protuberance. Slit the dura mater in the midline and see its interior. Put fine probes and identify the veins opening into it. These veins drain the cerebrum.
Arachnoid granulations: These are fine grape like structures projecting into the venous lacunae by the side of the superior sagittal sinus. These are projections of the arachnoid mater. The cerebrospinal fluid located in the subarachnoid space is poured into the venous sinus here.
Falx cerebri: Identify this from the crista galli to the level of external occipital protuberance. Cut it near the crista galli and pull it up to the tentorium cerebelli. Cut the tentorium cerebelli inner to the attached margin (Central part of the tentorium lies between the cerebrum and cerebellum). Ease the cerebellum from the posterior cranial fossa and feel the foramen magnum and medulla oblongata. Nearer to foramen magnum pull the falx cerebelli posteriorly and lift the cerebellum and medulla oblongata from the posterior cranial fossa. Carefully lift the temporal and occipital lobes. Put a scissors along the inner surface of the petrous part of temporal bone and cut the facial, vestibulocochlear, trigeminal, glossopharyngeal, abducent, vagus and accessory nerves. Put the scissors near the foramen magnum along its sides and cut the vertebral arteries and hypoglossal nerves. Slowly carefully lift up the whole brain. In this removal the whole brain is removed along with the arachnoid mater and all blood vessels and nerves. Along with the brain the central part of the tentorium cerebelli comes off. So it can be pulled out after the removal, and put it back in the anatomical position and can be studied.
Alternative Method to Remove the Brain in Two Pieces
Study of the Tentorium Cerebelli (Fig. 58)
Look for the glistening dura mater. It is a fold of the meningeal layer of the dura mater. It has got an attached margin along the inner side of the occipital bone from the internal occipital protuberance to the petrous part of the temporal bone, along the superior border of the petrous part of the temporal bone to the posterior clinoid process. Free margin of tentorium cerebelli is a ‘U’ shaped margin and anteriorly it is attached to the anterior clinoid process.
Straight sinus: Locate this at the junction of superior sagittal sinus with the tentorium cerebelli.
Transverse sinus: Slit the tentorium cerebelli along the attached margin of the tentorium cerebelli with the occipital bone. Observe the transverse sinus.
Inferior sagittal sinus: See this in the free margin of the falx cerebri and identify the formation of straight sinus by the union of inferior sagittal sinus and great cerebral vein of Galen.
Observe the hindbrain. See the cerebellum in the posterior cranial fossa. Note the midbrain, pons and medulla oblongata anterior to the cerebellum. Push the brainstem posteriorly. Note the oculomotor, trochlear, trigeminal, facial and vestibulocochlear nerves. Cut them nearer to the bone. Push the medulla oblongata further and cut the 6, 9,10,11,12 cranial nerves and the vertebral artery nearer to the foramen magnum and jugular foramen.
Push the brainstem and cerebellum forwards, pull the falx cerebelli backwards and cut the medulla oblongata near the foramen magnum and lift the hindbrain. This will remove the hindbrain along with all the cranial nerves from 3rd to 12th and the vertebral artery along with pia and arachnoid mater.
Middle meningeal artery: Note this bulging artery within the lateral aspect of the dura mater. Note its branches supplying the dura mater. Trace it down to its emergence from the foramen spinosum.
INTERIOR OF SKULL (Fig. 59)
After removing the brain, the interior of the skull which now is still covered by the dura mater, the arteries, dural venous sinuses and cranial nerves can be studied.
Vertebral artery: This enters the cranial cavity through the foramen magnum. Note the cut end of this artery within the foramen magnum.
Internal carotid artery: Note this artery lateral to the optic chiasma. This artery enters the cranial cavity through the carotid canal, passes through the cavernous sinus (will be dissected soon. and enters the brain lateral to the optic chiasma.
Sphenoparietal sinus: This sinus lies along the lesser wing of sphenoid. This drains into cavernous sinus.
Cavernous sinus: This sinus lies lateral to the pituitary gland. The oculomotor, trochlear, ophthalmic and mandibular division of trigeminal nerve lie in the lateral wall of the cavernous sinus.
Internal carotid artery and abducent nerve lie within the cavernous sinus. Locate them. Anterior, posterior and intercavernous sinuses connect the cavernous sinuses of either side.
Superior petrosal sinus: Slit the attached margin of the tentorium cerebelli along the petrous part of the temporal bone and note that it connects the cavernous sinus to the transverse sinus.
Inferior petrosal sinus: Locate this sinus from the cavernous sinus to the jugular foramen. It can be seen as a blue line. Slit it open and see the sinus.
Basilar plexus of veins: Locate these through the dura mater over the basilar part of the occipital bone.
- I. Olfactory nerve: This enters the skull as 20 rootlets through the cribriform plate of ethmoid bone. Note these openings in the ethmoid bone. It carries olfactory sensations.
- II. Optic nerve: Trace it in the optic canal. It carries visual sensations.
- III. Oculomotor nerve: This is a thick nerve passing through the free margin of the tentorium, into the lateral wall of the cavernous sinus to the superior orbital fissure. It is a motor nerve. It supplies the muscles of eyeball.
- IV. Trochlear nerve: This is a thin nerve. Locate it between the free and attached margins of the tentorium cerebelli passes along the lateral wall of the cavernous sinus to the superior orbital fissure. It is motor to superior oblique muscle of eyeball.
- V. Trigeminal nerve: It is a thick nerve, locate it in the posterior cranial fossa. It pushes the dura mater into the middle cranial fossa forming a covering to itself called the cavum trigeminal. Slit the dura mater and locate the ganglion and its branches.Ophthalmic division is the most superior of the divisions. It passes along the lateral wall of the cavernous sinus to the superior orbital fissure. It is a sensory nerve to the face.Maxillary division is the middle branch of the trigeminal nerve. It runs along the lateral wall of the cavernous sinus. It is sensory to the maxilla.Mandibular nerve leaves the cranial cavity through the mandibular foramen. It is a mixed nerve. Locate the deeper motor part of this nerve. It supplies muscles of mastication and is sensory to the face and mandible.
- VI. Abducent nerve: Locate this thin nerve piercing dura mater of posterior cranial fossa. It passes through the cavernous sinus along with the internal carotid artery. Trace it to the superior orbital fissure.
- VII and VIII. Facial and vestibulocochlear nerve: These nerves enter the internal auditory meatus in the petrous part of the temporal bone. Locate the fine labyrinthine artery in the posterior cranial fossa which accompanies these nerves.
- IX, X and XI. Glossopharyngeal, vagus and accessory nerves: They enter the jugular foramen. Locate the spinal part of the accessory which ascends up through the foramen magnum to join the cranial part of the accessory nerve.
- XII. Hypoglossal nerve: Locate this nerve passing through the hypoglossal canal just above the foramen magnum.
BONY ORBIT (Fig. 60)
Study the bony orbit on the dry skull. Note that it is a pyramidal shaped area. Its medial walls are parallel to each other whereas its lateral walls diverge laterally. Locate the followings:
Optic canal is formed by the two roots of the lesser wing of the sphenoid and the body of the sphenoid.
Superior orbital fissure is formed by the lesser wing and greater wing of sphenoid.
Inferior orbital fissure formed by the greater wing of sphenoid, maxilla and the zygomatic bone.
Anterior, posterior ethmoid canals are fine canals between the ethmoid and the frontal bone.
Internal orifice in the zygomatic bone is a fine foramen in the zygomatic bone.
Trochlea is a rough part on the medial part of the roof.
Supraorbital foramen or notch can be felt in the supraorbital margin.
SUPERFICIAL STRUCTURES OF THE ORBIT
Orbital periosteum envelops the contents of the orbit. The orbit has the lacrimal gland, eyeball with the optic nerve, muscles to move the eyeball, sensory nerves to supply the internal structures and skin, autonomic fibres to supply the interior of eyeball and the ophthalmic artery with its accompanying veins. You will identify all these structures as and when they appear in dissection (Fig. 62).
Trochlear nerve: Trace this most medial nerve into the superior margin of the superior oblique muscle nearer to its origin. Trace this nerve back to the lateral wall of the cavernous sinus. It supplies the superior oblique muscle.
Frontal nerve: This is the thick nerve seen right in the middle. Trace it back to the ophthalmic division of trigeminal nerve. Note that it immediately divides into two branches, the medial supratrochlear branch and thick lateral supraorbital nerve. Trace the nerves forwards along the superior orbital margin to the scalp. It is sensory to scalp.
Lacrimal nerve: It is a thin lateral branch along the superiolateral margin. Trace it back to the ophthalmic division and trace it forward to the lacrimal gland. Trace a fine zygomatic branch joining this nerve. The zygomatic branch brings in secretomotor fibres from the maxillary nerve to the lacrimal gland.
Lacrimal gland: It secretes tears. It is a light yellow color gland located on the anterolateral aspect of the orbit. It is divided into a superficial and a deeper part by the aponeurosis of the levator palpebrae superioris muscle. Locate this gland and identify its parts.
MUSCULATURE OF THE ORBIT
Orbit lodges the four recti, two oblique which act on the eyeball and a palpebral muscle which elevates the upper lid. The significant feature here is that the recti arise from a common tendinous ring located proximally near the superior orbital fissure. They all insert into the anterior half of the eyeball. Note that they move anterolaterally to reach their insertion. The oblique are inserted into the posterior half of the eyeball and they run anteroposteriorly.
Superior oblique muscle: Locate this muscle along the superomedial margin of the orbit. It arises from the common tendinous ring. Trace it to the trochlea at the anterior end and feel it. It is inserted into the superolateral surface of the eyeball posterior to the equator (you will see the insertion after reflecting the other muscles). Locate its nerve supply from the trochlear nerve.
Levator palpebrae superioris: Identify this muscle which occupies the whole central area. It arises from the under surface of the orbital plate of the frontal bone and is inserted into the upper eyelid. Note the deeper fibres inserted into the conjunctiva. The muscle fibres spread out as they move forwards. Note that it elevates the upper eyelid by pulling it.
Superior rectus: Note this muscle immediately deep to the levator palpebrae superioris. It arises from the tendinous ring. Note the margin from where it arises. Trace its insertion into the superior part of the eyeball in front of the equator. It is an elevator of the cornea.
Medial rectus muscle: Locate this muscle along the medial side of the orbit. It arises from the tendinous ring and gets inserted into the medial side of the eyeball. It is an adductor of the eyeball.
All the three muscles are supplied by upper division of the oculomotor nerve. The nerve enters into the muscles on their deeper aspect.
DEEP STRUCTURES OF ORBIT (Fig. 63)
Insertion of superior oblique: Trace this muscle from the level of the trochlea. Note that the muscle becomes aponeurotic and spreads out. It is inserted into the superolateral surface of the eyeball posterior to the equator. Clean the orbital fat and trace the insertion. Note that this muscle pulls the posterior part of the eye all upwards and medially and produces downward and lateral movement of the cornea
Nasociliary nerve: Clear the fat in the orbit and locate the nasociliary nerve crossing the optic nerve from lateral to medial. Trace it back to the ophthalmic division and forwards to the ethmoid between medial rectus and superior oblique muscles. This is the sensory nerve to the orbital structures and the ethmoidal air sinuses. It gives off fine anterior and posterior ethmoidal nerves which pass through the canals in the ethmoid bone. The anterior ethmoidal nerve after supplying the ethmoidal air sinus enters the nasal cavity to supply the mucous membrane of nose. The nasociliary reaches the face as the infratrochlear nerve and supplies the skin of the face.
Lateral rectus muscle: Locate this muscle along the lateral side of the orbit. It arises from the tendinous ring and is inserted into the lateral aspect of the eyeball. It is an abductor and is supplied by the abducent nerve.
Abducent nerve: Locate this nerve into the inner aspect of the muscle. Trace it backwards to the superior orbital fissure and the cavernous sinus.
Optic nerve: Locate this thick nerve entering into the orbit through the optic canal. It is the sensory nerve to carry the visual sensations.
OPHTHALMIC ARTERY (Fig. 64)
Locate this artery inferior to the optic nerve in the optic canal. Trace it forwards and see all its fine branches. It divides into a lacrimal branch which moves forwards and into the eyelid after supplying the lacrimal gland. The medial branch crosses the optic nerve either superficial or deep to the nerve. As it crosses the nerve it gives off ciliary branches to supply the eyeball. The central artery of retina enters the optic nerve while the ophthalmic artery lies deep to the optic nerve. It is an end artery and supplies the retina. The ophthalmic artery further runs medially and parallel to the medial wall of the orbit. Here it gives off the ethmoidal branches to enter the ethmoidal canals. They supply the ethmoidal air sinuses. The supraorbital is an independent branch. The ophthalmic artery gives the medial palpebral artery, to the lids, supratrochlear artery to the scalp and dorsal nasal to the nose. Throughout its course it gives off branches to supply the orbital structures.
Veins in the orbit exhibit a plexiform arrangement and leave the orbit as superior and inferior ophthalmic veins. The superior ophthalmic vein accompanies most of the branches of the artery and leaves through the superior orbital fissure and drains into cavernous sinus. The inferior ophthalmic vein drains the inferior structures and leaves it through the inferior orbital fissure. This drains into the pterygoid plexus of veins.
Ciliary ganglion is a parasympathetic ganglion. Pull the optic nerve medially and locate this small ganglion between it and the lateral rectus. Very near the apex of the orbit. You can see it suspended by the nasociliary and inferior division of oculomotor nerve.
Locate the short and long ciliary nerves arising from the ganglion and from the nasociliary nerve. Trace them reaching the back of the eyeball. These carry the autonomic and sensory fibres to the muscles within the eyeball.
Inferior oblique muscle: Locate this muscle in the floor extending from medial to lateral side. It arises from the medial aspect of the floor of the orbit. It is inserted into the inferolateral surface of the eyeball, posterior to the equator. It pulls the posterior aspect of the eyeball downwards and medially thus resulting in the upward and lateral movement of the cornea.
Inferior rectus muscle: Depress the inferior oblique muscle and pull the eyeball up and locate this muscle in the undersurface of the eyeball. It arises from the fibrous tendinous ring on its inferior aspect. It is inserted into the eyeball on its inferior surface anterior to the equator.
Inferior division of oculomotor nerve: Locate this nerve lateral to the optic nerve. It enters into the orbit through the superior orbital fissure. Trace it back to the oculomotor nerve. Trace its branches entering into the inferior rectus and inferior oblique muscles on their internal surfaces.
Maxillary nerve: Trace this nerve from the middle cranial fossa through the foramen rotundum to the floor of the orbit. Trace it into the infraorbital groove/canal.
Facial sheath of the eyeball: Pull the eyeball upwards and locate the connective tissue sheath from below the eyeball to the medial and lateral bony walls. They are called medial and lateral palpebral ligaments. All the muscles of the eyeball get inserted into the eyeball through this facial sheath.
LACRIMAL APPARATUS (Fig. 66)
The lacrimal apparatus manufactures tears, pours it on to the eyeball to moisten the eyeball. The excess tears are drained to the nasal cavity.
Lacrimal apparatus consists of lacrimal gland with its excretory ducts—this lies within the orbit, conjunctival sac—this is the space between the two eyelids and the eyeball, lacrimal papillae and puncta—these lie within the medial ends of the eyelid, the lacrimal canaliculi—these run from the puncta to the lacrimal sac, the lacrimal sac—this lies deeper to the medial palpebral ligament, the nasolacrimal duct—this drains the lacrimal sac to the inferior nasal meatus.
Many of these structures are small and deeply placed and are difficult to identify. The structures are described at the appropriate place.
The part of the nose that is seen externally is external nose. Feel it and note that it is both bony and cartilaginous. But when it is cut in the midline the total area extending from the anterior nasal aperture to the posterior choanae is considered as the nasal cavity.
Nasal cavity is a respiratory passage. It is divided into two parts by a septum. The surface area of the nasal cavity is increased by bony projections. The bones surrounding the nasal cavity are pneumatic bones, filled with air. They help in the resonance of the voice. The part seen externally is called the external nose. It is made up of both bone and cartilage. All the bones and cartilages of the nasal cavity are covered by the mucoperiosteum. The function of the cavernous tissue is to control the temperature of the passing air. It warms in cold climate and cools in warm climates. The roof of the nasal cavity is olfactory in nature and is supplied by the olfactory nerves.
It is divided into two halves by the median nasal septum. Note that it is made up of bone as well as cartilage. Identify the ethmoid, vomer and the space for the septal cartilage.
Observe that the lateral wall exhibits projections called conchae. Note that the wall is made up of maxilla, lacrimal, ethmoid, palatine, sphenoid and inferior nasal concha. Note the sphenopalatine foramen in the vertical plate of the palatine bone between its two roots. Note the area for cartilage.
See the median septum in the section and feel that it is covered by mucoperiosteum.
Identify the roof that is sloping both anteriorly as well as posteriorly.
Floor: The floor of the nasal cavity is same as the roof of the oral cavity. It is formed by the palate (It will be studied at a later stage of dissection).
Choanae is the posterior margin of the nasal cavity where it is continuous with the nasopharynx. It is bounded by the roof, lateral wall, septum and floor of the nasal cavity.
LATERAL WALL OF NOSE (Fig. 70)
Vestibule It is the depressed area immediately internal to the anterior nasal aperture. Note the small thick hairs called vibrissae. The vestibule is bounded superiorly by the limen nasi. The area above the limen is the atrium. It is limited superiorly by agger nasi an elevation. The atrium lies continuous with the middle meatus.
Conchae: These are the bony elevations seen in the lateral wall. They are generally three in number—the superior, middle and inferior conchae. The superior and middle are projections of the ethmoid bone and the inferior is an individual bone. Put a fine forceps and identify the gaps, the meatuses. The nasal cavity is surrounded by air sinuses, superiorly, posteriorly and laterally. These sinuses open into the meatuses. Feel the thick membrane covering the conchae. These are cavernous in nature, i.e. they are filled with capillary plexus.
PTERYGOPALATINE GANGLION (Fig. 71)
Pterygopalatine ganglion is a parasympathetic ganglion. It is connected to the maxillary nerve by two roots. It carries both general sensory fibres and secretomotor fibres. See the two roots and the pterygopalatine ganglion hanging down from the maxillary nerve. Trace the nerve of the pterygoid canal entering into the ganglion. These carry the preganglionic secretomotor fibres. Trace the branches arising from the pterygopalatine ganglion. The greater and lesser palatine nerves descend down and reach the roof of the palate. The pharyngeal branch goes posteriorly, the nasal branches traverse forward and nasopalatine nerve crosses and reaches the septum.
MAXILLARY NERVE (Fig. 72)
The maxillary nerve reaches the pterygopalatine fossa through the foramen rotundum. It moves forward into the floor of the orbit. See the posterior superior alveolar nerves that it gives off before reaching the orbit. They supply the maxillary teeth and the maxillary air sinus.
Arterial supply is by maxillary artery. The third part of the maxillary artery reaches the pterygopalatine fossa after passing through the infratemporal fossa. It accompanies the maxillary nerve in the pterygopalatine fossa. It continues as the infraorbital artery in the floor of the orbit. Locate this artery and its branches in the pterygopalatine fossa. It gives off posterior superior alveolar, greater palatine, lesser palatine, nasopalatine, pharyngeal and artery accompanying the nerve of the pterygoid canal. Study of air sinuses and meatuses.
STUDY OF AIR SINUSES AND MEATUSES (Fig. 73)
Sphenoethmoidal recess: This is the space above and posterior to the superior concha. The sphenoidal air sinus opens into this. Locate this in the body of the sphenoid bone. It is divided into two halves by and unequal septum. Pass a probe from the sinus to the sphenoethmoidal recess.
Superior meatus: Identify this deep to the superior concha. The posterior ethmoidal air cells open into this. Cut the superior concha with a scissors. Note that two to three air cells open into it. Put a probe into them and note that they belong to posterior group of ethmoidal air cells. There are around 8 to 10 cells on the ethmoid bone. They are grouped into posterior middle and anterior group.
Middle meatus: It is the space deeper to the middle concha. Cut the middle concha with a scissors very near its attachment. Note the bulla ethmoidalis. It is a bulge in the center of the meatus. Note 2 to 3 air cells opening into it. Put a probe through them and note they are in the center of the ethmoid bone. These are middle ethmoidal air cells. Identify the groove below the bulla ethmoidalis. This is the hiatus semilunaris. It receives frontal, ethmoidal and maxillary air sinuses.
Put a probe into the anterior end of the hiatus and push it up and note that they are continuous with the air cells in the anterior part of the ethmoid through a small infundibulum. These are the anterior ethmoidal air cells.
Frontal air sinus: Put another probe through the cut frontal air sinus into the anterior end of the hiatus semilunaris through the infundibulum.
Maxillary air sinus: It occupies the whole maxilla (identify this on a dry skull. Identify its opening in the floor of the hiatus semilunaris. Pass a probe downwards and note its depth. Note that the rear premolars and molars project into it). Realize the mechanical disadvantage of this sinus, as its opening is above the base, due to this, the maxillary air sinus gets often infected.
Inferior meatus: Note that it is widest of all meatuses. It receives the nasolacrimal duct. It is nearer to the anterior end of the meatus. Pass a fine probe into the nasolacrimal duct. It passes through the bony wall to reach the lacrimal sac in the medial end of the orbit. Feel the lacrimal sac.
Neurovascular bundle of the nasal cavity: Nasal cavity is supplied by the branches of the maxillary nerve and maxillary artery. They reach the nasal cavity through the pterygopalatine fossa.
The palate is made up of hard palate and soft palate. The hard palate separates the nasal cavity from the oral cavity. The soft palate separates the nasopharynx from the oropharynx. The midline posterior projection from the soft palate is called the uvula.
Hard palate: It is made up of bones. Identify the bones forming the hard palate on a dry skull. They are maxilla and the palatine bone.
The mouth has two parts—the vestibule and the oral cavity. The vestibule lies external to the teeth and the oral cavity lies between the maxilla and mandible. The partition between the nasal cavity and oral cavity is formed by the hard palate. The oral cavity lodges the tongue.
Vestibule (Fig. 76): This is the area between the cheeks laterally and maxilla and mandible medially. The parotid duct opens into it opposite to the upper second molar tooth. If possible try to locate its end (this can be seen well in a living subject).
Dorsum of the tongue is the superior surface facing the hard palate (See all the parts in a living person also). Note the sulcus terminalis near the posterior part. It is a V shaped sulcus which separates the anterior 2/3rd from posterior 1/3rd. In the anterior 2/3 note the fine filiform papillae.
See the rounded fungiform papillae between the filiform papillae. Locate the circumvallate papillae behind the sulcus. In the remaining part of the posterior 1/3—note the grooves. These grooves receive the openings of the deeply placed glands. The elevations between the grooves is due to the lymphoid tissue.
Ventral surface of tongue: Lift the tongue up and note the frenulum in the midline, fimbriated fold laterally and sublingual fold and orifice of the submandibular duct in the floor (see these in a living person).
MUSCLES OF TONGUE (Fig. 79)
Muscles of tongue can be divided into intrinsic and extrinsic muscles. The muscles are bilateral and are separated by a central fibrous septum. The intrinsic muscles have no bony attachment.
In a paramedian section of the tongue the intrinsic muscles can be identified. They are arranged as: Superior longitudinal layer lies immediately beneath the dorsum of the tongue. Vertical muscle fibres run down vertically. Horizontal fibres intermingle with the vertical fibres. Inferior longitudinal fibres lie below these above muscles.
Genioglossus: This is the extrinsic muscle from the superior genial tubercle lies between the inferior longitudinal fibres and genial tubercles. This is a fan-shaped muscle. It is a depressor of the tongue (other extrinsic muscles will be seen in a later dissection).
Fauces (Fig. 80): It is the junction between the oral cavity and the oropharynx. It is formed by two pillars—the anterior palatoglossal fold and posterior palatopharyngeal fold. Between the two pillars the palatine tonsil is located.
The pharynx is a funnel shaped fibromuscular tube extending from the base of the skull to the 6th cervical vertebra. It is divided into three parts—the nasopharynx, oropharynx and laryngopharynx (Fig. 81).
Boundaries: The roof of nasopharynx is formed by the sphenoid bone. It is continuous with the nasal cavity anteriorly. The junction is called the choanae. The lateral wall shows the auditory opening. Inferiorly and anteriorly it is separated from the oral cavity by the soft palate. Posteriorly and inferiorly it is continuous with the oropharynx. The roof of the oropharynx is same as the floor of the nasopharynx. Oropharynx is continuous with the oral cavity anteriorly and superiorly. Anteriorly and inferiorly the sloping posterior 1/3rd of tongue forms the boundary. The junction between the oropharynx and oral cavity is called the oropharyngeal isthmus. It is formed by the palatoglossal fold. The lateral wall forms fauces and lodges tonsil. The laryngopharynx is continuous with the larynx anteriorly. The opening into the larynx is called inlet of the larynx. The laryngopharynx lies behind and parallel with the larynx. It continues below as the esophagus.
It is the common passage for air and food. Its interior is covered by mucous membrane. Structurally, the pharynx has four layers. Innermost mucosal layer, followed by submucosal layer, the external muscular layer, covered by adventitial layer.
Nasopharynx: See the position of the pharyngeal tonsil. It is the collection of lymphoid tissue in the roof of the pharynx. It can easily be identified deeper to the mucous membrane. Identify the opening of the auditory tube in the lateral wall. It is a longitudinal slit with anterior and posterior walls. The posterior wall is more prominent and is called tubal elevation. It is due to tubal tonsil, the aggregation of the lymphoid tissue here. A mucosal fold continues down from the tubal elevation and is called the salpingopharyngeal fold. The fold is raised by the salpingopharyngeal muscle.
SOFT PALATE (Fig. 82)
Soft palate is the posterior part of the palate and it is muscular. It is made up of five muscles. Two muscles can be seen from above and two muscles from below and one muscle posteriorly.
Tensor veli palatine: Identify this muscle lateral and anterior to the auditory tube. It runs vertically on the external side of the auditory tube. It arises from the scaphoid fossa lateral side of auditory tube and spine of the sphenoid (identify them on the dry skull). It hooks round the pterygoid hamulus and gets inserted in the form of an aponeurosis which forms the core for the soft palate. It is a tensor of the soft palate. Nerve supply. It is supplied by the mandibular near trunk just below the foramen ovale (this was identified in the infratemporal fossa dissection).
Levator veli palatine: It arises from the undersurface of the petrous part of the temporal bone and the medial surface of the cartilage of the auditory tube. It is inserted into the superior surface of the palatine aponeurosis. It is an elevator of the palate.
Musculus uvulae: Strip the mucous membrane over the uvula and locate this centrally located muscle. It arises from the spine and gets into the mucous membrane.
Salpingopharyngeus: This muscle is the longitudinal muscle of the pharynx. It arises from the lower part of the auditory tube and is inserted into the posterior border of thyroid cartilage. Pull the muscle up and feel the insertion and its action as an elevator of larynx.
Palatoglossus muscle: This muslce forms the anterior pillar of the fauces. This is an extrinsic muscle of the tongue arising from the soft palate. It arises from the undersurface of the palatine aponeurosis. It is inserted into the side of the tongue.
Palatopharyngeus muscle. This muscle forms the posterior pillar of the fauces. It arises from the posterior border of the hard palate and the palatine aponeurosis. It runs downwards and is inserted into posterior border of the thyroid cartilage. This is also an elevator of the larynx.
Passavant's muscle: Few of the fibres of the palatopharyngeus muscle run straight back to the midline raising an elevation in the lateral wall. It acts like a sphincter between nasal and oral pharynx, along with the soft palate.
Nerve supply: All the muscles of the pharynx and the soft palate are supplied by the cranial accessory nerve through the pharyngeal plexus located in the pharyngeal wall except the tensor veli palatine which is supplied by the mandibular nerve.
Tonsil: Note this lymphoid tissue between the palatoglossal and palatopharyngeal fold. It shows pitted appearance.
OROPHARYNX (Fig. 83)
Anteroinferior wall of the oropharynx: This is formed by the posterior part of tongue. Note the following structures by pushing the tongue forwards.
Median glossoepiglottic fold: It is a raised mucosal fold in the midline extending from the back of the tongue to the center of the epiglottis.
Lateral glossoepiglottic folds: These are two lateral mucosal folds to the right and left of the median fold.
Vallecula: It is the central depression between the median and lateral glossoepiglottic folds.
Laryngopharynx It coexists with the larynx, in other words, the larynx forms the anterior wall to this part of the pharynx (this will be studied with larynx).
STUDY OF THE STRUCTURES FROM THE LATERAL ASPECT (Fig. 84)
The pharynx extends from the basiocciput to the 6th cervical vertebra. It is covered by adventitial layer. Clean this connective tissue and try to identify the following structures from above downwards on the lateral aspect. This is the external circular muscular layer. It is made up of three muscles one fitting into the other, like buckets.
Superior constrictor muscle: It is the upper circular muscle of the pharynx. Identify the muscle. It arises from the medial pterygoid plate, pterygomandibular raphae and mandible behind the third molar tooth. At its upper border identifies the anterior tensor veli palatini and posterior levator veli palatini with the auditor tube in between.
Middle constrictor muscle: Locate this muscle lying deeper to the hyoglossus. It arises from greater, lesser cornu of the hyoid bone and the lower part of the stylohyoid ligament. The fibres span out posteriorly to reach the midline.
Inferior constrictor muscle: Note this muscle below and external to the middle constrictor. It arises from the oblique line of thyroid cartilage and from the lateral side of the cricoid cartilage. It is Inserted into the midline raphae located posteriorly.
All the three constrictors of pharynx insert into a median raphae posteriorly. They are supplied by cranial accessory nerve through the pharyngeal plexus.
Pharyngeal plexus: It is a plexus of nerves deep to the pharyngeal fascia. It is formed by the (i) pharyngeal branch of the vagus, but it carries the cranial accessory fibres. Thus it receives through a communication near the jugular foramen. These fibres supply the muscles of pharynx and soft palate. (ii) Pharyngeal branch of glossopharyngeal nerve. It is sensory to the mucous membrane. (iii) pharyngeal branch of superior cervical sympathetic ganglion. This carries vasomotor fibres to the blood vessels of the pharynx.
Larynx is an organ of voice production. It extends from the 4th to 6th cervical vertebrae. It is around 5 cm long, 4 cm in width and 3.5 cm in anterior posterior diameter. It is a fibrocartilaginous structure. It has an obliquely placed inlet of the larynx. It opens into the pharynx.
NEUROVASCULAR BUNDLE (Fig. 85)
Internal laryngeal nerve and superior laryngeal vessels: These enter the larynx through the thyrohyoid membrane. Superior laryngeal artery is a branch of superior thyroid and nerve is a branch of superior laryngeal nerve. This nerve is sensory above the rima glottidis. External laryngeal nerve is a branch of the superior laryngeal, branch of the vagus nerve.
Inferior laryngeal artery and the recurrent laryngeal nerve: Trace these two structures entering into the larynx between trachea and esophagus below the inferior constrictor muscle. The recurrent laryngeal nerve is a motor nerve to muscles of larynx and sensory to mucous membrane below the rima glottidis.
Hyoid bone: This forms the superior boundary of the larynx. It has got a wide body in the center, greater cornua extending laterally and lesser cornua at the junction of body and greater cornua.
Thyrohyoid membrane: Identify this membrane extending between the upper border of hyoid bone to the upper border of thyroid cartilage. It shows two thickenings medial (in the midline) and lateral (towards the ends) thyrohyoid ligaments.
Thyroid cartilage: This cartilage has two laminae. They unite anteriorly in the midline to form an angle. This is called Adams apple or laryngeal prominence. It is around 90° degrees in males and 120° in females. It has two horns, the superior and inferior horns. The inferior horn articulates with the cricoid cartilage.
Cricothyroid ligament: Feel this ligament between the thyroid and cricoid cartilage on the anterolateral aspect. Push the back of the forceps and note that it is attached to the inner aspect of the thyroid cartilage near its middle.
Cricoid cartilage: Feel the broad posterior lamina of the cricoid cartilage and the anterior arch shaped part. Totally it resembles a signet ring.
Arytenoid cartilages: Feel these pyramidal shaped cartilages on the superior surface of the cricoid cartilages. Feel its three surfaces, the medial, lateral and the base. It has three angles, the superior (articulating with corniculate cartilage), the anterior is called vocal process and lateral is called muscular process.
Corniculate cartilage: It is a comma shaped cartilage articulating with the superior angle of arytenoid.
Cuneiform cartilage: Feel it. It is a nodule in the aryepiglottic fold.
Epiglottis: Identify this leaf shaped cartilage on the posterior aspect of the hyoid and thyroid cartilages. It can easily be bent forwards and backwards. It is connected to the hyoid by hyoepiglottic ligament and to the thyroid by thyroepiglottic ligament.
Quadrangular membrane: You clasp this membrane between your fingers. It extends from the anterior border of the arytenoid cartilage to the side of the epiglottis. As the name signifies it is quadrangular in shape. It has a superior border called aryepiglottic ligament. This forms part of inlet of larynx. Its inferior free border forms the vestibular ligament. The quadrangular membrane separates the vestibule of the larynx from the piriform fossa, the space between the larynx and the thyroid cartilage.
INLET OF LARYNX
Turn the larynx to its posterior aspect and observe and feel the inlet of the larynx. It is formed by the upper border of the epiglottis, aryepiglottic folds, arytenoids cartilages and interarytenoid mucous membrane.
MUSCLES (Fig. 88)
Posterior cricoarytenoid: Identify this muscle on the posterior aspect of the lamina of cricoid cartilage. It arises from the same and is inserted into the muscular process of the arytenoids cartilage. Note that the fibres are transverse in the upper part, these act as lateral rotators, and the lower fibres slope up, and these would pull the arytenoid downward thus producing abduction.
Oblique arytenoid: See it between the two arytenoids. It arises from the posterior aspect of one arytenoid and is inserted into the apex of the other arytenoid. Note that the fibres of both sides cross each other like an x. It acts along with aryepiglottis muscle to close the inlet of the larynx.
Transverse arytenoid: This muscle is deeper to the oblique arytenoid. It extends from one arytenoids to the other arytenoid. This muscle acts as an adductor.
Aryepiglottic muscle: Trace this muscle in the free margin of aryepiglottic fold. It arises from the apex of the arytenoids to be inserted into the side of the epiglottis. The aryepiglottis along with the oblique arytenoid acts like a scissors and closes the inlet of the larynx.
Cricothyroid: See this on the lateral aspect. It arises from the lateral aspect of the cricoid cartilage and is inserted into the lower border of the thyroid cartilage. It is a tensor of the vocal cords. It is supplied by the external laryngeal nerve.
Lateral cricoarytenoid muscle (Fig. 89): Trace this deeper muscle. It arises from the upper border of the cricoid cartilage. It is inserted into the muscular process. It is an abductor of vocal cords.
INTERIOR OF LARYNX (Fig. 90)
Rima vestibuli: It is the lower border of the quadrangular membrane. It is thickened at its lower part and is called vestibular ligament. It is covered by mucous membrane called vestibular folds. The gap between the two vestibular folds is called the rima vestibuli.
Rima glottidis: It is the gap between the two vocal ligaments. The thickened upper end of the cricothyroid membrane is called the vocal ligament. The mucous membrane covering it forms the vocal fold. The gap extending from the back of the thyroid cartilage to the posterior wall is called the rima glottidis. It has got an anterior intermembranous part and posterior intercartilaginous part between the two arytenoid cartilages.
Saccule: Put a probe through the sinus and extend it upwards. This is an extension of the sinus lateral to the quadrangular membrane. In birds it is very much well developed.
Vestibule: It is the part of the larynx, above the rima vestibuli to the inlet of the larynx. See its anterior wall, is far higher and formed by the epiglottis.
Cornea: Cornea is the outer protective coat. It forms the anterior 1/6th of the outer coat of the eyeball. It is transparent.
Sclera: It forms the posterior 5/6th of the outer coat of the eyeball. It is the opaque thick fibrous layer.
Vitreous body: This is the innermost jelly like body. It is enclosed by a thin capsule. It generally gets cut and falls off when the eyeball is cut.
Retina: This is the nervous layer of the eye. It looks whitish in the cut eyeball. It easily gets peeled off from the deeper choroid layer. It becomes very thin anteriorly.
Vascular layer: It is the intermediate layer. Peel the retinal layer and look at his layer. It is black in color. Iris is its anterior part and this lies in front of the lens. Ciliary body—this is the part lateral to the lens. Choroid—this is the part behind the ora serrata. Ora serrata—is the serrated junction between the ciliary body and choroid. This can easily be identified.
Zonule: Note this suspending fibrous structure extending from the ciliary body to the lens.
Lens: This is the biconvex structure suspended by the zonular fibres.
MUSCLES OF THE EYEBALL
Ciliary muscle: Locate this muscle within the ciliary body.
The sphincter and dilator pupilae: These are the muscles present within the iris. You can see these muscles in the cut parts of the ciliary body and iris. These muscles are supplied by the autonomic nervous system, through the ciliary ganglion.
Optic disc and optic nerve: Identify these structures at the posterior medial part of the eyeball.
Anterior ciliary arteries: These arteries enter the sclera near the sclerocorneal junction. The posterior ciliary arteries pierce the sclera around the optic nerve. All the arteries are branches of the ophthalmic artery.
Venae vorticose: These are the veins draining the eyeball. They pierce the eyeball near the equator and drain into ophthalmic veins.