THE VESICUL^ SEMINALES 491 



and is termed the ligament of the epidiclj'mis. The other cord, the gubernaculum 

 testis, extends from the tail of the epididymis to the subperitoneal tissue in the 

 vicinity of the future vaginal ring. The deferential fold (Plica ductus deferentis) 

 is given off from the inner face of the mesorchiuni, and joins the urogenital fold 

 jiosteriorly. Tlie l)ody of the epididymis at this time lies in the edge of an oblique 

 fold formed by the outer layer of the mesorehium. After tlie middle of fa-tal life, 

 a pouch or diverticulum of the peritoneum, the processus vaginalis, grows downward 

 through the inguinal canal, carrying with it cremaster fibers derived from the 

 internal oblique muscle and a layer from the transversalis fascia. It is accom- 

 panied by an inguinal extension of the gubernaculum testis. The latter blends 

 below with the subcutaneous tissue which later becomes the dartos. The tail of 

 the epididymis first enters the processus vaginalis, followed by the testicle with its 

 mesorehium, which descends within this diverticulum of the peritoneum until it 

 reaches the scrotum. The vas deferens and its fold descend synchronously with 

 the epididymis and testicle. 



The mechanical factors concerned in the migration of the testicle are matters on which 

 much uncertainty still exists. That the gubernaculum exerts sufficient traction to guide the 

 epididymis and testicle to the inguinal canal seems plausible. The internal inguinal ring may 

 constitute a locus minoris resistentia^ in the abdominal wall, especially after the descent of the 

 processus vaginalis. Progressive shortening of the gubernaculum was formerly considered to be 

 the chief cause of the descent through the abdominal wall. Increase in the intra-abdominal 

 pressure is probably an important factor. 



In the foal the descent of the testicles is often complete at birth, but it fre- 

 quently happens that one testicle or both may be retained in the inguinal canal or 

 in the abdomen for some months. In other cases the testicle may return into the 

 canal or abdomen, since in the young foal the vaginal ring is large and the testicle 

 small and soft, and not yet closely anchored by the scrotal ligament. In rare cases 

 the descent may be completed as late as the fourth year (personal observation) . 



Indefinite retention of one testicle or both in the abdominal cavity or inguinal canal is not rare 

 in horses; this condition is termed cryptorchism. Abdominal retention is the more usual form 

 of cryptorchism in adult horses, inguinal retention being usually temporary. The retained 

 testicle is usually, but not always, small, thin, soft, and flabby, and is non-spermiogenic. The 

 processus vaginalis and the inguinal part of the gubernaculum are usually present, but may be 

 rudimentary. The ligament of the epididymis and the corresponding part of the mesorehium 

 are often so long that the tail of the epididymis may be several inches distant from the testicle. 

 The abdominal part of the gubernaculum may be 8 to 10 inches (ca. 20 to 25 cm.) long, and the 

 ligament of the epididymis much elongated (10 to 1.5 cm. in length according to Vennerhohn); 

 thus the testicle may have a wide range. The vaginal ring is sometimes closed. 



In many mammals the testicles normally remain in the abdominal cavity; such animals are 

 termed testiconda, and include the elephant, some insectivora, hyrax, sloths, ant-eaters, armadillos, 

 and cetacea. In others the testicles descend periodically during the period of oestrum, and then 

 return into the abdomen, or they may be extruded and retracted voluntarily; this is true of most 

 rodents, many insectivora (moles, shrews, hedgehog), and bats. 



THE VESICULAE SEMINALES 



The vesiculae seminales (Fig. 394) are two elongated and somewhat pj riform 

 sacs, which lie on either side of the posterior part of the dorsal surface of the blad- 

 der. 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 pos- 

 teriorly. 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.' 



' Sometimes one vesicula or both are very large in the gelding. The writer has seen four 

 cases in the dissecting room, three of which were bilateral, the other unilateral. The vesicula re- 

 sembled the urinary bladder in appearance and contained about a quart of thick, amber-colored 

 secretion. 



