392 EMBRYOLOGY. 



(fig. 224 A). This gradually penetrates the abdominal wall and 

 enters into a fold of the skin, which is developed in the pubic region, 

 as will be shown in a subsequent section (see fig. 231 gw). The 

 opening of the hernia-like evagination, which leads into the body- 

 cavity, is called the inner inguinal [abdominal] ring (Ir) ; the portion 

 which traverses the musculature of the abdominal wall, the inguinal 

 canal; and the blind end which is expanded within the dermal fold, 

 the scrotum. 



In its migration the testis (fig. 224 JB) also sinks down into this 

 peritoneal fold, whereby it remains undetermined whether HUNTER'S 

 ligament exercises an influence on it or not. The entrance into the 

 inguinal canal usually takes place in the eighth month, into the 

 scrotum in the ninth month, so that at the end of embryonic life 

 the descent is, as a rule, completed. The canal then closes by 

 fusion of its walls, and thereby the testis comes to lie in a sac 

 constricted off from the abdominal cavity and enclosed on all 

 sides. 



The various enveloping structures of the testis also become intelli- 

 gible from the sketch of the development just given. Since the 

 cavity which shelters it is simply a detached portion of the body- 

 cavity, it is, as a matter of course, lined by peritoneum (fig. 224 4 '). 

 This is the so-called tunica vaginalis propria, on which, as on other 

 regions of the peritoneum, we have to distinguish a parietal layer 

 ( 4 ') lining the wall of the sac and a visceral layer ( 4 ") investing the 

 testis. Outside of this follows the tunica vaginalis communis ( 3 ') ; 

 it is the evaginated, and at the same time extraordinarily attenu- 

 ated, layer of muscles and fasciae ( 3 ) of the abdominal wall. Con- 

 sequently it also contains some muscle -fibres enclosed in it, which 

 are derived from the musculus obliquus abdominis internus, and 

 constitute the suspensory muscle of the testis or cremaster. 



In the descensus testiculorum, which should normally be com- 

 pleted in Man at the end of embryonic life, interruptions may, under 

 certain circumstances, occur and produce an abnormal location of the 

 testis, which is known under the name of cryptorchism. The descent 

 remains incomplete. Then the testes of the recently born child are 

 either found to be located in the body-cavity, or they still stick fast 

 in the wall of the abdomen, in the inguinal canal. In consequence 

 the scrotum feels small, flabby, and flaccid. 



Such anomalies are designated as inhibition-malformations, because 

 they are explained by the fact that the processes of development 

 have not reached their normal termination. 



