586 GENITAL ORGANS OF THE BULL 
Except at its origin and termination the urethra is provided with a continuous 
layer of striped muscle, placed outside of the erectile tissue. This is described as 
consisting of two parts or muscles. 
(1) The urethral muscle (M. urethralis)' encloses the wide pelvic part of the 
urethra, and covers the bulbo-urethral glands. It consists of longitudinal and 
transverse fibers. It is a compressor of the pelvic part of the urethra and the bulbo- 
urethral glands. By its forcible contraction it plays an important réle in the ejacula- 
tion of the seminal fluid, and also in evacuating the last of the urine in micturition. 
(2) The bulbo-cavernosus muscle (M. bulbocavernosus)” is the continuation 
of the urethral muscle on the extrapelvic part of the urethra; it extends from the 
ischial arch to the glans penis. At the root of the penis it is the thickest, and 
forms a complete layer of circular fibers which enclose the corpus cavernosum 
urethre. Beyond this it diminishes very gradually in thickness, and consists of 
fibers which arise on a median ventral raphé and curve around the corpus cavernosum 
urethra to end on the tunica albuginea of the corpus cavernosum. Its action is to 
empty the extrapelvic part of the urethra. 
The ischio-urethral muscles (Fig. 577) are small bands which arise on the 
ischial arch and crura of the penis and pass forward to become lost on the ventral 
layer of the urethral muscle. They may assist in erection of the penis by exerting 
pressure on the dorsal veins. 
GENITAL ORGANS OF THE BULL 
The scrotum is situated somewhat further forward than in the horse. It is 
ovoid, but compressed from before backward, is long and pendulous, and has a well- 
marked neck when not contracted. The skin here is usually flesh-colored, but in 
some breeds it is more or less pigmented; it is sparsely covered with short hairs. 
Just in front of it are four (sometimes only two) rudimentary teats. 
The testicles are relatively larger than those of the horse, and have an elon- 
gated, oval outline. The long axis is vertical, the attached border being posterior. 
The medial surface is somewhat flattened. A testicle of an adult bull measures on 
the average about four or five inches (10 to 12 em.) in length, exclusive of the epi- 
didymis; with the latter the length is about six inches (15 em.). The width is 
about two and a half to three inches (ca. 6 to 8 cm.), and the anterior-posterior 
diameter about the same. The weight is about ten to twelve ounces (ca. 300 grams). 
The tunica albuginea is thin; it contains many elastic fibers, but no unstriped 
muscle. The parenchyma is yellowish in color. The mediastinum testis is an 
axial strand of connective tissue (about 5 mm. in thickness), which descends from 
the upper part of the attached border deeply into the gland. From it the chief 
trabecule radiate, but distinct interlobular septa are not present. The seminif- 
erous tubules form in the mediastinum a network, the rete testis. The efferent 
ducts from the rete, a dozen in number, leave at the upper end of the mediastinum. 
The epididymis is very closely attached to the testicle along the posterior 
border of the latter. The head is long; it curves over the upper extremity and 
about a third of the way down the anterior border of the testicle; it is covered by 
an extension of the tunica albuginea. The body is very narrow, and lies along the 
lateral part of the posterior border of the testicle, to which it is attached by a narrow 
peritoneal fold. The tail is large and is closely attached at the lower extremity of 
the testicle. 
The spermatic cord and the tunica vaginalis are much longer than in the horse; 
1Formerly termed Wilson’s muscle. 2 Formerly called the accelerator uri. 
