DESCENT OF THE TESTICLES 577 



abnormally large and allow a loop of bowel to enter the cavity of the tunica vaginalis. It is large 

 in the young foal. In the gelding it is smaller and sometimes partiaUy occluded. In man the 

 cavity is almost always obliterated early, except in its scrotal portion, tlius abohshing the vaginal 

 • ring and the inguinal part of the cavity. 



DESCENT OF THE TESTICLES 



During early foetal life the testicle is situated against the dorsal wall of the 

 abdominal cavity, in contact with the ventral surface of the corresponding kidney. 

 As growth proceeds it gradually migrates from this primitive position, and finally 

 passes down the inguinal canal into the scrotum. Previous to its descent through 

 the abdominal wall the testicle is attached to the sublumbar region by a fold of 

 peritoneum, termed the mesorchium. This fold contains the vessels and nerves 

 of the testicle in its anterior border. In its posterior edge is the elongated tail of 

 the epididymis, and two cords of fibrous tissue and unstriped muscle. One of these 

 cords is short and connects the tail of the epididymis with the testicle; later it 

 becomes shorter, and is termed the ligament of the epididymis. The other cord, 

 the gubemaculxim testis, extends from the tail of the epididymis to the subperi- 

 toneal tissue in the vicinity of the future vaginal ring. The deferential fold (Plica 

 ductus deferentis) is given off from the medial face of the mesorchium, and joins the 

 genital fold posteriorly. The body of the epididymis at this time lies in the edge 

 of an oblique fold formed by the lateral layer of the mesorchium. After the middle 

 of foetal life a pouch 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 

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

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

 the epididymis and testicle. In the foal the descent of the testicles is often com- 

 plete at birth, but it frequently 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 vagina! 

 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. 



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 abdominal inguinal ring may 

 constitute a locus minoris resistentiae 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 protjably an important factor. 



Indefinite retention of one testicle or both in the abdominal cavity or ingumal 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-spermiogemc. 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 mesorchium 

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

 The abdominal part of the guberilaculum may be eight to ten inches (ca. 20 to 25 cm.) long, and the 

 ligament of the epididymis much elongated (10 to 15 cm. in length, according to Vennerholm) ; 

 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. 

 37 



