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 partially occluded. In man the 
cavity is almost always obliterated early, except in its scrotal portion, thus abolishing 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 gubernaculum testis, extends from the tail of the epididymis to the subperi- 
toneal tissue in the vicinity of the future vaginal rmg. 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 mguinal 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 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. 
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 resistentiz# 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. 
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 eryptorchism 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 
Tudimentary. 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 gubernaculum may be eight to ten inches (ca. 20 to 25 em.) long, and the 
ligament of the epididymis much elongated (10 to 15 em. 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 pericdically during the period of cestrum, and then 
return into the abdomen, or they may be extruded and retracted voluntarily; this is true of most 
rodents, any insectivora (moles, shrews, hedgehog), and bats. 
