Page 466 - Anatomy and Physiology of Farm Animals, 8th Edition

Anatomy of the Male Reproductive System / 451

necessary for supporting growth and sinusoids predominating over connective
tissue. An erection of the equine penis
VetBooks.ir differentiation of the accessory sex results in the transformation of the penis
glands at puberty and their maintenance
from a flaccid consistency to a rigid shape,
while sperm production is concomitant.
Prolonged exposure of the prostate with a concurrent increase in girth as the
gland to testosterone can result in excess sinusoids fill with blood.
growth of the prostatic tissue that is not The two crura of the penis are the prox-
cancer (benign prostatic hyperplasia). imal parts of the corpora cavernosa. They
In older intact male animals, the originate on the caudal surface of the
enlarged prostate gland manifests ischial arch, one on each side of the sym-
clinically as difficulty voiding urine. physis of the pelvis. The ventral midline
groove between the corpora cavernosa
Bulbourethral Glands contains the penile urethra and an associ-
ated unpaired body of erectile tissue, the
corpus spongiosus. The proximal continu-
The bulbourethral (formerly Cowper’s)
glands are paired glands on either side of ation of the corpus spongiosum is the bulb
of the penis, which lies between the crura.
the pelvic urethra just cranial to the ischial In most animals, the corpus spongiosum
arch but caudal to the other accessory penis is continuous distally with the
glands. Bulbourethral glands are especially erectile tissue of the glans.
large in the boar.
In dressing a carcass for human con-
sumption, the penis is removed. Removal
Penis of the penile crura leaves two round
marks on the ischial arch. These are
The male organ of copulation, the penis, called pizzle eyes, and their presence is
may be divided into three general areas: used to identify a dressed carcass as
the glans, or free extremity; the main male.
portion, or body; and the two crura, or The glans penis shows considerable var-
roots, that attach to the ischial arch of the iation from species to species. The horse
pelvis (Fig. 24‐11). and sheep both have a free portion of the
The bulk of the penile body’s internal urethra, the urethral process, that projects
structure is composed of paired columns beyond the glans. The bull and ram have a
of erectile tissue, the corpora cavernosa. helmet‐shaped glans, and the external ure-
Each corpus cavernosum is replete with thral opening of the bull opens into a
blood sinusoids divided by sheets of twisted groove. The penis of the boar has a
connective tissue called trabeculae. These twisting cranial extremity and only a small
are derived from the tunica albuginea, a glans (Fig. 24‐12).
heavy, fibroelastic capsule surrounding the Erection of the penis occurs when more
penis. In species with a fibroelastic penis blood enters the penis by way of the arte-
(ruminants and swine), the trabeculae rial supply than leaves by the veins. The
form the bulk of the penis, and as a conse- increased blood volume enlarges the penis
quence, in these species the penis is firm and makes it turgid. In the stallion, whose
when not erect. The bull, boar, and ram penis is musculocavernous, the penis
have a sigmoid shape to the penis such becomes much larger in all dimensions
that when an erection is achieved, the upon erection. The fibroelastic penis (as
retractor penis muscle relaxes allowing found in ruminants and swine) does not
the penis to straighten at the sigmoid increase much in diameter during erection
flexure. As a result, the fibroelastic penis and requires significantly less blood to
functionally increases in length to allow for achieve an erection. Instead, the chief
intromission. In contrast, the stallion has a effect of erection of the penis in ruminants
musculocavernous penis, with the blood consists of lengthening the penis by