Digestion and Absorption — Bio Zoology STD 11 — Question

The large intestine consists of the caecum, colon, and rectum. The caecum is a small blind pouch-like structure that opens into the colon and it possesses a narrow finger-like tubular projection called the vermiform appendix.
Both caecum and vermiform appendix are large in herbivorous animals and act as an important site for cellulose digestion with the help of symbiotic bacteria. The colon is divided into four regions – an ascending, a transverse, a descending part, and a sigmoid colon.

The colon is lined by dilations called haustra (singular – haustrum) (Figure). The “S” shaped sigmoid colon (pelvic colon) opens into the rectum. Rectum is concerned with temporary storage of feces. The rectum open out through the anus. The anus is guarded by two anal sphincter muscles. The anal mucosa is folded into several vertical folds and contains arteries and veins called anal columns. Anal column may get enlarged and causes piles or haemorrhoids.