The =vesiculæ seminales= (Fig. 394) are two elongated and somewhat
pyriform sacs, which lie on either side of the posterior part of the
dorsal surface of the bladder. They are partly inclosed in the
urogenital fold, and are related to the rectum dorsally. Their long axes
are parallel with the vas deferentia and converge posteriorly. Each
consists of a rounded blind end, the =fundus=, a middle, slightly
narrower part, the =body=, and a posterior constricted part, the =neck=
or =duct=.
In the stallion they are about six to eight inches (ca. 15 to 20 cm.)
long, and their greatest diameter is about two inches (ca. 5 cm.); in
the gelding they are usually much smaller.[145]
The vesiculæ are, for the most part, retroperitoneal, but the fundus
extends forward into the urogenital fold and hence has a serous
covering. The =neck= or =duct= (Ductus excretorius) dips under the
prostate, and usually unites with the end of the vas deferens to form
the =ejaculatory duct=.
[Illustration: