Upper respiratory tract consist of nasal cavity, nasopharynx and oro pharynx, development of which is discussed with development of face, nasal cavity and alimentary tract. Lower respiratory tract consisting of larynx, trachea, principal bronchi and intrapulmonary bronchial tree, develops from laryngotracheal diverticulum arising from cranial part of foregut. Epithelium and glands of respiratory tract develop from endoderm of laryngotracheal diverticulum: while the other layers of the tract develop from surrounding mesoderm. Lung: Laryngotracheal diverticulum (respiratory diverticulum) divides into two bronchial buds. Each bronchial bud surrounded by condensation of mesoderm forms the lung bud. Lung develops from the lung bud. Bronchial buds go on dividing to form intrapulmonary bronchial tree right up to alveoli. Intraembryonic coelom is divided into three parts from which various body cavities develop. (i) Pericardial cavity- pericardial cavity, (ii) Pericardioperitoneal canals—pleural cavities, and (iii) Peritoneal cavity- Peritoneal cavity. Lesser sac: The lesser sac of peritoneal cavity develops in three parts as follows: (i) Right pneumo enteric recess in dorsal mesogastrium, (ii) After rotation of stomach part of peritoneal cavity lying behind stomach and lesser omentum, and (iii) The cavity between two layers of graeter’s omentum. Diaphragm: The diaphragm develops from four elements. (i) Septum transversum, (ii) Pleuroperitoneal membrane, (iii) Dorsal and ventral mesentery of oesophagus, and (iv) Body wall.