Page 468 - Anatomy and Physiology of Farm Animals, 8th Edition

Anatomy of the Male Reproductive System / 453

Muscles of the Male Genitalia
VetBooks.ir 1 Bull The urethral muscle (m. urethralis) is the

striated muscle associated with the pelvic
portion of the urethra. It completely encir-
2
cles the urethra of the goat and horse but
surrounds only the ventral and lateral aspects
Bull
of the bovine, porcine, and ovine urethra.
The urethral muscle forms the voluntary
sphincter of the urinary bladder; during ejac-
Ram ulation, waves of peristaltic contractions in it
help propel the semen through the urethra.
The extrapelvic continuation of the
urethral muscle is a striated muscle called the
Boar bulbospongiosus muscle. It surrounds the
urethra and bulb of the penis. The bulbospon-
giosus muscle of the horse extends from the
penile bulb between the crura of the penis
along the entire urethra to the glans penis. In
Stallion other animals it covers the urethral bulb and
extends only a short distance along the penile
Figure 24-12. Free end of the penis. (1) Bull urethra. The bulbospongiosus muscle contin-
penis prior to intromission. (2) Bull penis follow- ues the action of the urethral muscle in emp-
ing intromission. Spiraling of the glans is a normal tying the urethra by peristaltic contractions.
consequence of erection. Source: Hafez and Hafez, The ischiocavernosus muscles are
2000. Reproduced with permission of John Wiley
& Sons, Inc. paired striated muscles that cover the
superficial aspect of the crura of the penis.
The two muscles converge from their
origins on the lateral sides of the ischial
straightening the sigmoid flexure, much as arch toward the body of the penis. When
a bent garden hose tends to straighten these muscles contract, they pull the penis
when water pressure increases. dorsocraniad against the bony pelvis, aid-
ing erection by compressing much of the
venous drainage from the penis.
Prepuce The retractor penis muscles are paired
smooth muscles that take origin from the
The prepuce is an invaginated fold of ventral aspect of the first few caudal verte-
skin surrounding the free extremity of the brae. These muscles pass ventrad on each
penis. The outer surface is fairly typical side of the anal canal, then continue on the
skin, while the inner mucous membrane midline of the penis superficial to the
consists of a preputial layer lining the urethra. For the fibroelastic penis, these
prepuce and a penile layer covering the muscles must relax for an erection to occur.
surface of the free extremity of the penis.
The prepuce of the horse makes a double
fold, so two concentric layers surround Blood and Nerve Supply
the penis when it is retracted. The pre- of the Male Genitalia
puce of the pig has a diverticulum dorsal
to the preputial orifice. It accumulates The testis derives its blood supply from the
urine, secretions, and dead cells, which testicular artery, which branches directly
contribute to the typical odor of a from the abdominal aorta a short distance
mature boar. caudal to the renal artery of the same side.