Parts of gastrointestinal system are stomach, duodenum, jejunum, ileum, cecum, appendix, ascending, transverse, descending, sigmoid colon, rectum, anal canal, liver, gallbladder, pancreas, spleen. Peritoneum is a large serous membrane lining abdominal cavity. It is in the form of a closed sac, invaginated by many viscera. Mouth consists of vestibule, lips, cheek, gums, teeth, palate, tongue, salivary glands (parotid, submandibular, sublingual). Histology of these parts is illustrated.