The =scrotum= is situated about half-way between the inguinal region and
the anus. The skin covering it is pigmented and is covered sparsely with
fine hairs. The raphé is not very distinct.
The =testicles= are relatively small, and have a round-oval form. The
long axis is oblique, and is directed upward and backward. The
mediastinum testis is central and is well developed. The epididymis is
large, and is closely attached along the outer part of the dorsal border
of the testicle.
The =spermatic cord= and the =tunica vaginalis= are long; they cross the
side of the penis very obliquely. The upper end of the tunic is
sometimes closed, so that there is then no vaginal ring. The vasa
deferentia have very narrow ampullæ.
The =vesiculæ seminales= are absent; hence there are no ejaculatory
ducts.
The =prostate= is relatively large; it is yellowish in color, dense in
structure, and lies at the anterior border of the pubis. It is globular,
and surrounds the neck of the bladder and the urethra at their junction.
A faint median furrow indicates a division into two lateral lobes. The
capsule and stroma contain a large amount of unstriped muscle. The ducts
are numerous. Lobules of prostatic tissue (pars disseminata) are also
found on the urethra further back. The gland is subject to much
variation in size, and is often enlarged, especially in old subjects.
The =uterus masculinus= is a very small saccule (Utriculus prostaticus),
often difficult to find.
The =bulbo-urethral= (Cowper’s) =glands= are absent.
The =penis= presents several special features. In its posterior part
there are two distinct corpora cavernosa, separated by a median septum
penis. In its anterior part there is a bone, the =os penis=, which in
large dogs reaches a length of four inches (ca. 10 cm.) or more. It is
regarded as a continuation forward of the corpus cavernosum. Ventrally
it is grooved for the urethra; dorsally it is convex, and anteriorly it
becomes smaller and has a curved fibrous prolongation. The =glans penis=
is very long, extending over the entire length of the os penis;
posteriorly it forms a rounded enlargement, the =bulbus glandis=;
anteriorly it is cylindrical, smaller, and pointed at the extremity.
Just in front of the bulbus glandis there is a thick circular layer of
glands, forming the =annulus glandularis= (Schmaltz). The two dorsal
veins arise from the bulbus glandis, pass backward on the dorsum penis,
and unite at the ischial arch. A small muscle (M. compressor venæ
dorsalis penis) arises from the tuber ischii on either side; the two
converge on the dorsum penis near the bulbus glandis. They compress the
dorsal veins, and may also tend to elevate the penis and thus assist in
copulation. The other muscles offer no features worthy of special
description.
The =prepuce= forms a complete sheath around the anterior part of the
penis. The outer layer is ordinary integument. The inner layer has the
character of a glandular mucous membrane; it is thin and reddish in
color. The penile layer is glandless. In the fundus of the præputial
cavity there are numerous lymph follicles. The protractor muscles arise
in the xiphoid region and decussate posteriorly around the extremity of
the penis.
[Illustration:
FIG. 405.—EXTERNAL GENITAL ORGANS OF MALE DOG, VENTRO-LATERAL VIEW OF
PREPARATION.
_1_, Scrotum; _1′_, tunica vaginalis; _2_, epididymis; _3_, vascular
part of spermatic cord; _4_, vas deferens; _5_, prepuce; _6_, glans
penis; _6′_, corpus cavernosum penis; _7_, bulbus glandis; _7′_,
contour of bulbus in erection; _8_, ischio-cavernosus muscle; _a_,
acetabulum; _b_, obturator foramen. (After Ellenberger, in
Leisering’s Atlas.)
]
[Illustration: