12 THE TESTIS AND ITS RELATION TO REPRODUCTION 



(2) an evagination of the peritoneum into each of the abdominal out- 

 pocketings which act as peritoneal linings for each pocket. 



It is worthy of mention that the above outpushings of the abdominal wall 

 and of the peritoneum precede the movement of the testes into the scrotum. 

 They serve to illustrate the theory that a shortening of the gubernaculum is 

 not sufficient to explain testis descent. Rather, that in this descent a whole 

 series of developmental transformations are involved; the shortening of the 

 gubernaculum and scrotal development merely represent isolated phases of 

 the general pattern of movement and growth associated with this descent. 



More recent research emphasizes the importance of certain physiological 

 factors relative to the descent problem. It has been determined, for example, 

 that administration of the gonadotrophic hormone of pregnancy urine (cho- 

 rionic gonadotrophin) or of the male sex hormone, testosterone, aid the 

 process of extra-abdominal descent (i.e., descent from the inguinal ring area 

 downward into the scrotum). Hormone therapy, using chorionic gonadotrophin 

 together with surgery, is used most often in human cryptorchid conditions. 

 The androgen, testosterone, aids testicular descent mainly by stimulating the 

 growth of the scrotal tissues and the vas deferens; however, it is not too 

 successful in effecting the actual descent of the testis (Robson, '40; Wells, 

 '43; Pincus and Thimann, '50). 



The phenomenon of testicular migration thus is an unsolved problem. 

 Many activities and factors probably play a part in ushering the testis along 

 the pathway to its scrotal residence. 



3. General Structure of the Scrotum and the Testis in Mammals 

 a. Structure of the Scrotum 



The scrotal modification of the body wall generally occurs in the postero- 

 ventral area between the anus and the penial organ. However, in marsupials 

 it is found some distance anterior to the latter. 



Each scrotal evagination consists of three general parts: the skin with 

 certain attendant muscles, the structures of the body wall below the skin, 

 and the peritoneal evagination. The skin, with its underlying tunica dartos 

 muscle tissue and superficial perineal fascia, forms the outer wall of the 

 scrotum (fig. 6). Within this outer cutaneous covering lie the two body-wall 

 and two peritoneal evaginations. The body-wall evaginations involve con- 

 nective and muscle tissues of the external oblique, internal oblique, and 

 transversus muscles. The caudal part of each peritoneal outpocketing forms 

 the serous cavity or inguinal bursa in which the testis is suspended after its 

 descent, and its more anterior portion forms the inguinal canal (figs. 2, 

 4B, 6). The oblique and transversus layers of tissues thus are molded into 

 a musculo-connective tissue compartment around each serous cavity. The 

 median septum of tfie scrotum represents the area of partial fusion between 



