_1_, Prostate gland (pars disseminata); _2_, urethra; _3_, urethral
muscle; _4_, aponeurosis. The lumen of the urethra is black.
]
The structure of the vesicula is masked by a thick capsule of fibrous
tissue and unstriped muscle, which maintains it in its bent condition
and also sends trabeculæ between the alveoli. There is a central canal
into which the secretion formed in the alveoli passes. The cavities
(central canal and alveoli) are lined with columnar epithelium. On
account of this structure the term glandulæ vesiculares is preferred
by some anatomists.
The =prostate= is pale yellow in color, and consists of two parts. The
=body= (Corpus prostatæ) is a mass which stretches across the dorsal
surface of the neck of the bladder and the origin of the urethra. It
measures about an inch and a half (ca. 3.5 to 4 cm.) transversely, and
about half an inch (ca. 1 to 1.5 cm.) in width and thickness. The =pars
disseminata= surrounds the pelvic part of the urethra; dorsally it forms
a layer about half an inch (ca. 10 to 12 mm.) thick, but ventrally it is
quite thin. It is concealed by the urethral (Wilson’s) muscle; hence it
often escapes notice, but is very evident on cross-section (fig. 402).
The =prostatic ducts= open into the urethra in rows between two folds of
the mucous membrane which proceed backward from the colliculus
seminalis.
The =uterus masculinus= appears to be absent frequently. Ellenberger
states that it opens between the ejaculatory ducts, while Martin says
that it usually has two orifices at the colliculus, but that it often
unites with the vasa deferentia.
The =bulbo-urethral= (Cowper’s) =glands= are somewhat smaller than in
the stallion. They are liable to escape notice, since they are covered
by a thick layer of dense fibrous tissue and also partially by the
bulbo-cavernosus muscle. Each has a single duct which opens into the
urethra under cover of a fold of the mucous membrane.
The =penis= is cylindrical, and is longer and of very much smaller
diameter than in the horse. Just behind the scrotum it forms an
=S=-shaped curve, the =sigmoid flexure=; thus about one foot is folded
up when the penis is fully retracted. The flexure is effaced during
erection. The =glans penis= is about three inches (ca. 8 cm.) in length.
It is flattened dorso-ventrally, and its extremity is pointed and
twisted. The =external urethral orifice= is situated at the end of a
groove formed by this twist; it is only large enough to admit a probe of
medium size. Even in the non-erect state the penis is remarkably dense
and firm. The =tunica albuginea= is very thick, and incloses the
urethra. In the first part, as far as the first curve, there is a thick
median =septum penis=. Beyond this there is a central axial rod of dense
fibrous tissue from which numerous strong trabeculæ radiate. The
erectile tissue is small in amount, so that the organ undergoes very
little enlargement in erection.
The length of the penis in the adult is about three feet (ca. 90 cm.).
The crura are flattened laterally. The suspensory ligaments are
attached to the ventral ridge on the symphysis. The body is somewhat
flattened dorso-ventrally beyond the first curve. The extremity of the
glans is unsymmetrical, the urethral orifice being situated
ventro-laterally. The glans contains little erectile tissue, and hence
undergoes little enlargement in erection.
The =bulbo-cavernosus muscle= presents several remarkable features. It
is for the greater part an inch or more (ca. 3 cm.) in thickness, but
its length is only six to eight inches (15 to 20 cm.). It is covered by
a strong aponeurosis, and is divided by a median raphé into two lateral
halves except at its origin. It diminishes in size from behind forward,
and its anterior extremity is pointed.
The =ischio-cavernosus muscle= resembles in general that of the horse,
but is flattened laterally. It is covered by a close aponeurosis.
The =retractor penis= muscle resembles that of the horse in origin. Its
two parts are about an inch (ca. 2 to 5 cm.) apart on the root of the
penis, where they lie in a groove on either side of the
bulbo-cavernosus. They then come close together and pass on either side
of the ventral curve of the sigmoid flexure. Further forward they lie
along the ventral aspect of the penis, and end about five or six inches
(ca. 12 to 15 cm.) behind the glans.
The =prepuce= is very long and narrow. Its orifice is about two inches
(ca. 5 cm.) behind the umbilicus; it is only large enough to admit a
finger readily, and is surrounded by long hairs. The cavity of the
sheath is about fifteen inches (35 to 40 cm.) long, and a little over an
inch (ca. 3 cm.) in diameter. The lining membrane forms longitudinal
folds; it is covered with squamous stratified epithelium, and has coiled
tubular glands. The penile layer is glandless, and is reddish in color.
It presents lymph nodules in its posterior part.
There are two pairs of =preputial muscles= which are derivatives of the
panniculus carnosus. The anterior pair, the =protractors= of the prepuce
(Mm. præputiales craniales), are two flat bands, two inches or more (5
to 6 cm.) in width, which arise close together in the xiphoid region,
about eight inches (20 cm.) in front of the preputial orifice. Traced
backward they diverge, leaving the umbilicus and an area about one and a
half inches wide free, and then unite behind the preputial orifice. They
draw the prepuce forward. The posterior pair, the =retractors= of the
prepuce (Mm. præputiales caudales), arise in the inguinal region and
converge on the anterior part of the prepuce. They draw the prepuce
backward.
These muscles are subject to a good deal of variation. The retractor
may be absent. Many fibers come in from the panniculus on either side,
dip under the protractor, and are inserted into the skin just behind
the preputial opening. The homologue of the protractor is present in
the cow.
The =urethra= in its pelvic part is about five inches (12 cm.) long, and
is of relatively small and uniform caliber. The =urethral= (Wilson’s)
=muscle= incloses the tube ventrally and laterally; it is very thick,
crescentic in cross-section, and is covered by an aponeurosis. Dorsally,
the aponeurosis is thick and the muscle absent. Inside of these the pars
disseminata of the prostate surrounds the urethra as far back as the
bulbo-urethral glands. The =colliculus seminalis= is short, but
prominent; from it the urethral crest extends forward to the trigonum
vesicæ. The extrapelvic part has an enlargement, the =bulb=, at its
origin; it then gradually diminishes in diameter, and is relatively very
small at its termination. Other features have been mentioned in
preceding paragraphs.
[Illustration: