IVRI Anatomy
A free veterinary anatomy learning platform for B.V.Sc., M.V.Sc., DVM and veterinary medicine students worldwide, developed at the Veterinary Anatomy Section, ICAR-Indian Veterinary Research Institute, Bareilly—covering VCI/MSVE and international university curricula through regional anatomy, histology, embryology, comparative biomechanics, clinical notes, quizzes and revision.
The rectum is the terminal part of the large intestine, lying in the pelvic cavity dorsal to the urogenital organs and ventral to the sacrum. It runs roughly straight (hence 'rectum'). The cranial portion is suspended by the mesorectum and covered by peritoneum; the caudal ~15 cm becomes retroperitoneal — this section can be torn during rough rectal palpation, leading to fatal peritonitis.
The anal canal is the very short terminal segment lined by stratified squamous epithelium. It is surrounded by two sphincters:
• Internal anal sphincter: smooth muscle, involuntary, autonomic control.
• External anal sphincter: striated muscle, voluntary, innervated by the caudal rectal nerves (branches of pudendal nerve) — paralysis after sacral fractures or epidural overdose.
Anus: The external opening, closed by the sphincters and surrounded by hairy skin. The mucocutaneous junction is called the anocutaneous line.
Vasculature & Innervation: Caudal rectal artery (from internal pudendal); innervation as above. The pelvic plexus on the lateral wall of the rectum carries parasympathetic fibres governing defecation.
| COW | Long, accessible per rectum — routine for pregnancy diagnosis, palpation of pelvic organs. |
| HORSE | Wall very thin and easily torn during rectal exam — major cause of euthanasia in clinical practice. |
| DOG | Short rectum. Anal sacs (paranal sinuses) lie at 4 and 8 o'clock — common site of impaction/abscess. |
| FOWL | No true anus — rectum opens into the cloaca, which has urodeum, coprodeum, proctodeum compartments. |
Explore the hidden mechanics of why structures are present, absent or modified across domestic and wildlife species—and how each anatomical design supports movement, function and clinical practice.
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