The Vesiculae Seminales

The vesiculæ seminales (Fig. ) 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.

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.

Structure.—The wall, exclusive of the partial serous coat, consists of a fibrous adventitia, a middle muscular coat, and a mucous lining. The muscular coat is thickest at the fundus, and consists of two planes of longitudinal fibers with a circular layer between them. The mucous membrane is thin, and is arranged in numerous folds which form a network; the spaces so inclosed present the openings of tubulo-alveolar glands. The epithelium is columnar. The blood-supply is derived from the internal pudic artery.