Urethra in Male Animals

The urethra in male animals serves as the common passage for the excretion of urine and the transportation of semen.

It is approximately 115 cm in length and consists of three distinct parts: the pelvic part, the bulb of the urethra, and the penile part.

In the bull, the pelvic part of the urethra is about 20 cm in length and is situated along the pelvic floor.

The pelvic urethra is enclosed by the urethral muscle (also known as Wilson’s muscle), which aids in ejaculation and micturition through its forcible contraction.

The bulb of the urethra is the extra-pelvic part, located at the ischial arch, and bends ventrally to the pelvis.

The penile urethra runs inside the penis proper. Urethral glands are present in humans, but they are absent in the bull, stallion, dog, and cat. However, in the bull and ram, there are many glands diffused over the urethra, known as the disseminate part of the prostate gland. These should not be referred to as urethral glands. In the boar, urethral glands are distinct and present.

Species Variations of the Urethra

The urethra of animals is a long, mucous tube that extends from the neck of the bladder to the tip of the glans penis.

Bull

The urethra of the bull passes backward on the floor of the pelvis, turns around the ischial arch forming a sharp bend, and then passes forward to be included in the body of the penis. It therefore has pelvic and extra-pelvic (or penile) parts. The pelvic part is 12 cm long and is relatively small and uniform in diameter. The urethral muscle encloses it ventrally and laterally and is very thick. It is related to the rectum and prostate above, the obturator muscles below, and the Cowper’s gland laterally. The extra-pelvic or penile part passes between the two crura of the penis, turns forward, and is included in the body of the penis.

Here, the corpus spongiosum and bulbo-cavernous muscle cover it. The tube forms an enlargement at its beginning, called the bulbus urethrae. It then gradually diminishes in diameter and becomes very small at its termination, forming the processus urethrae.

The opening from the bladder into the urethra is termed the internal urethral orifice, and it is closed except during urination. The terminal opening is known as the external urethral orifice.

The colliculus seminalis is a rounded prominence situated medially on the dorsal wall, about 5 cm behind the internal urethral orifice. On it are two slit-like openings situated close together. These are the ejaculatory orifices, where the vas deferens and the excretory duct of the seminal vesicle open.

The urethral crest is a median ridge of mucous membrane on the dorsal wall of the urethra. The crest extends forward from the colliculus, while two mucous folds pass backward from the colliculus. A little lateral and caudal to the colliculus are the openings of the prostate, and further back are the ducts of the Cowper’s gland.

Ram and Buck

The urethra lies in a groove on the ventral surface of the corpus cavernosum in the ram and buck.

Its terminal part projects commonly about an inch and a half beyond the glans penis, forming a twisted processus urethrae.

Stallion

The pelvic part is 10 to 12 cm long and 5 to 6 cm in diameter in the stallion. The extra-pelvic part is 1.5 cm in diameter.

The colliculus seminalis presents on either side a small diverticulum in which the vas deferens and the duct of the seminal vesicle open. Lateral to this are the openings of the prostatic ducts, and further back are openings of the ducts of the Cowper’s gland.

Boar

The urethra of the boar has a very long pelvic part and is covered by a thick urethral muscle, except dorsally where there is a dense fibrous layer.

Dog

The bulb of the urethra is well developed in the case of the dog.

Rabbit

The external urethral orifice is placed dorsally and slightly cranially in the rabbit.

Cock

The urethra is absent in the cock.