This tube (Ductus deferens) extends from the tail of the epididymis to
the ejaculatory duct. It passes upward in the inguinal canal, inclosed
in a fold detached from the inner surface of the mesorchium, near the
posterior (attached) border of the latter. At the vaginal ring it
separates from the other constituents of the spermatic cord, and turns
backward and inward into the pelvic cavity (Fig. 272). For some distance
it lies in the free edge of the urogenital fold, by which it is attached
to the lower part of the lateral wall of the pelvis. In its further
course (over the dorsal surface of the bladder) it leaves the edge of
the fold and inclines inward between its layers, coming in contact with
the inner face of the vesicula seminalis. Over the neck of the bladder
the two vasa lie very close together, flanked laterally by the necks of
the vesiculæ seminales, and having the uterus masculinus between them.
They then disappear under the isthmus of the prostate, and are continued
through the wall of the urethra by the =ejaculatory ducts=. The latter
are formed in the urethral wall by the union of the vas deferens with
the duct (or neck) of the corresponding vesicula seminalis; they are
thin-walled tubes, about 2 to 3 mm. long and 6 to 7 mm. wide, which open
into the urethra on either side of the colliculus seminalis. In about 15
per cent. of subjects the vas deferens and duct of the seminal vesicle
do not unite, but open side by side into the urethra. From its origin
until it reaches the dorsal surface of the bladder the vas deferens has
a uniform diameter of about a quarter of an inch (ca. 6 mm.). It then
forms a fusiform dilatation, the =ampulla ductus deferentis= (Fig. 394);
this part is about six to eight inches (ca. 15 to 20 cm.) long, and in
its largest part nearly an inch (ca. 2 cm.) in diameter in the stallion;
in geldings the dilatation is usually not very pronounced. Beyond the
ampulla the duct abruptly contracts.
=Structure.=—The wall of the vas deferens is thick and the lumen
relatively small, so that the tube has a firm and cord-like character.
It is covered with peritoneum, except in the last few inches of its
course. The loose =adventitia= contains numerous vessels and nerves. The
thick =muscular coat= consists of longitudinal and circular layers. The
=mucous membrane= has an epithelium of short columnar cells. In the
posterior part of the tube, and especially in the ampulla, there are
numerous tubulo-alveolar glands.
=Blood-supply.=—Spermatic and umbilical arteries.
=Nerve-supply.=—Spermatic and pelvic plexuses.