Dog / cleaning The buttocks, Which show the scrotum and anus. Dog / The buttocks of the dog, Which show the scrotum and anus. Education Chart of Biology for Male . The alimentary tract extends from the mouth to the anus. Most of the length of this tract is made up on the bowels, namely the small intestine and large intestine. The small intestine is divided into three parts – duodenum (leading from the stomach), jejunum and ileum (leading to the large intestine). The human anus (from Latin anus which are circular muscles that normally maintain constriction of the orifice and which relaxes as required by normal.