Cutaneous zone

The cutaneous zone is the terminal portion of the anal canal, extending from the intermediate zone to the anus.

Epithelium:

• Lined by keratinized stratified squamous epithelium, similar to skin.

• Contains hair follicles, sebaceous glands, and sweat glands.

Species-Specific Features

Dog

• Paranal sinuses (Anal sacs): Paired structures located on either side of the anus, lined by apocrine and sebaceous glands (gland of paranal sinuses). Open into the cutaneous zone at 4 and 8 o'clock positions.

• Circumanal (perianal) glands: Large modified sebaceous glands located in the skin around the anus. They are androgen-dependent and can give rise to circumanal gland tumors.

Cat

• Similar to the dog but smaller anal sacs.

• Circumanal glands are less prominent than in dogs.

Horse

• No distinct anal sacs.

• The cutaneous zone is smoother and has a less developed glandular structure compared to carnivores.

Ruminants (e.g., cattle, sheep, goats)

• Also lack anal sacs.

• The cutaneous zone has typical skin structures but fewer glandular modifications.

Vascular and Nervous Supply

• Blood supply: From branches of the internal pudendal artery.

• Innervation: Somatic innervation from the caudal rectal nerve, a branch of the pudendal nerve, providing sensory input to the region.

Functional Significance

• The keratinized epithelium and sweat/sebaceous glands provide protection and antimicrobial properties.

• In carnivores, anal sacs are used for scent marking and communication.