PENIS
The penis is the male copulatory organ that allows semen and urine to go through the penile urethra. The penis is made up of three compartments: 1) The roots (crura) of the penis begin at the caudal border of the pelvic ischial arch, 2) The body is a forward extension from the roots, and 3) the glans is a free extremity.
The corpus cavernosum, also called erectile tissue, is the cavernous tissue that makes up the majority of the interior structure and fills with blood during an erection. Surrounding the corpus cavernosum is a dense fibroelastic coating called the tunica albuginea, which also contributes to the sheets of connective tissue that are present within. Depending on the amount of connective tissue found in the corpus cavernosum, the penis is classified as musculocavernosus, which contains more cavernous space and less connective tissue, or fibroelastic having less cavernous space and more connective tissue. The musculo- cavernous penis is characteristic of the horse and dogs, and the fibroelastic penis is found in ruminants (cattle, sheep, goats) and pigs. During erection, the musculocavernous penis greatly increases in both length and girth as the cavernous spaces fill with blood, while in the fibroelastic penis, the increase in length is largely brought about by a straightening of the sigmoid flexure. The urethra is on the ventral aspect of the body of the penis and is surrounded by the corpus spongiosum. An evident urethral process is found in the ram and buck. The purpose of the urethral process in rams and bucks is thought to be to spray semen during ejaculation into the cervical region. The dog has a bulbus glandis at the caudal part of the glans. The enlargement of the bulbus glandis is responsible for prolonged retention of the penis during coitus, commonly known as the tie. The penis of bulls, rams, and boars has an S-shaped sigmoid flexure that gets extended during erection.The prepuce is an invaginated fold of skin that surrounds the free extremity of the penis. The stallion has a doublefolded pouch. Waxy accumulations, known as beans, sometimes form in the outer fold and must be removed manually. The boar has a preputial diverticulum (pouch) on the dorsal wall, which often contains decomposing urine and macerated epithelium.
20.5
Source:
Rana Tanmoy (ed.). Principles of Veterinary Animal Physiology. CRC Press,2026. — 290 p.. 2026
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