The Scrotum and Testes

The scrotum lies below the pubic brim, where it is concealed from lateral inspection by the thigh. It is broadly globular, commonly asymmetrical, and divided by an external raphe that extends cranially onto the prepuce and caudally onto the perineum.

The testes are imperfectly ellipsoidal, being slightly compressed from side to side (Fig. 22.19 and see Fig. 5.41). They generally lie with their long axes horizontal but become almost vertical on strong contraction of the cremaster muscles that attach to the vaginal tunic near the cranial poles. The tunica albuginea is less thick than in ruminants, and the testes yield on gentle compression. The grayish pink parenchyma is contained under some pressure and bulges through any incision of the tunic. The septa that extend inward from the capsule do not join to form a visibly distinct mediastinum. The epididymis lies along the dorsal border and projects a little beyond the poles of the testis, where it is most firmly attached. It leaves a distinct testicular bursa that opens laterally. The ligament of the tail of the epididymis is quite thick and must be severed in castration by the "open" method. Wartlike growths (appendices testis) on the testis near the head of the epididymis are very common; they are remnants of the paramesonephric duct.

The spermatic cord is broad and thin where it attaches to the testis but rounds when followed toward the superficial inguinal ring. The cranial vascular part (see Fig. 5.41/5) is clearly distinguished from the caudal part that carries the deferent duct. The constituents diverge in the usual manner on entering the abdomen (Fig. 22.19 and see Fig.

The wide inguinal canal makes inguinal hernias a relatively common occurrence.

Although the process of testicular descent may be presumed to be governed by the same factors (p. 163) as in other species, it is marked by one circumstance unique among domestic mammals. The testes of the fetal colt exhibit an inordinate though temporary increase in size between the 100th and 250th days of gestation, attaining a peak on about the 215th day. (A comparable enlargement affects the ovaries of the fetal filly.) In consequence, although each testis arrives in the vicinity of the vaginal ring on about the 120th day, it is delayed here and does not resume its migration until it has shrunk to a fraction of its maximal size. It does not arrive in the scrotum until close to the time of birth and may even arrive after this event (probably within 2 weeks either way).

Not infrequently a testis fails to reach the scrotum even then and remains hidden within the abdomen or delayed within the inguinal canal. Retention may be temporary or permanent, confined to one side or bilateral, and if bilateral, the sites of lodgment may be asymmetrical. The condition, known as cryptorchidism, may resolve spontaneously, and the testis may make a delayed appearance in the scrotum at some time within the first year of postnatal life or possibly even later. In such cases it may be assumed that the testis was held up within the inguinal canal because the vaginal ring normally contracts shortly after birth, preventing a late entry to the canal from the abdomen. Testes that fail to make an appearance within a reasonable time require surgical removal, for which a variety of techniques is available depending on the location of the arrest. The diagnosis of cryptorchidism is sometimes less obvious than might be supposed. Cryptorchid animals that have changed hands may be presented in good faith as geldings, and suspicion may only arise when stallion characteristics of conformation and behavior develop. Moreover, in young horses of nervous disposition, successfully descended testes may initially escape detection by being withdrawn into the groins, against the superficial inguinal rings, when the scrotum and inguinal regions are palpated.