THE ORGANS OF THE MIDDLE GERM-LAYER. 



391 



attention was directed to the non-striate muscle-fibres contained in 

 it, or a shortening of the connective-tissue cord by gradual shrinkage 

 was assumed. But it is impossible for this very important change 

 in position to have taken place in that manner. One therefore 

 rightly seeks to explain the agency of the ligament in another way, 

 without assuming an active shortening or a traction exercised by 

 muscular action. We have to do here simply with processes of 

 unequal growth. When, out of several organs originally lying beside 

 one another in the same region of the body, certain ones in later 

 months of embryonic life increase in size less, while others, on the 

 contrary, grow extraordinarily in length, the natural consequence is 

 that the more rapidly growing parts are shoved past those that grow 



Fig. 224. Two diagrams to illustrate the descensus and the formation of the envelopes of the 



testis. 

 A, The testis lies in the vicinity of the inner abdominal ring. B, The testis has entered the 



scrotum. 

 1, Skin of the abdomen ; 1', scrotum with tunica dartos ; 2, superficial abdominal fascia ; 2', 



COOPER'S fascia ; 3, muscle-layer and fascia transversa abdominis ; 3', tunica vaginalis 



communis with cremaster ; 4, peritoneum ; 4', parietal layer of the tunica vaginalis propria ; 



4", peritoneal investment of the testis or visceral layer of the tunica vaginalis propria.' 

 Ir, Inguinal or abdominal ring ; h, testis ; si, vas deferens. 



more slowly. If, now, in the present case the skeletal parts and 

 their accompanying muscles in the lumbar and pelvic regions become 

 elongated, while the Hunterian ligament does not grow and there- 

 fore remains short, the latter necessarily because one of its ends 

 is attached to the skin of the inguinal region and the other to the 

 testis draws down the testis as the movable part; it draws the 

 testis at first gradually into the cavity of the false pelvis, and finally, 

 when the other parts have become still larger, when at the same 

 time the abdominal wall has become much thicker, into the vicinity 

 of the inner abdominal ring (fig. 223). 



The testis migrates still farther in consequence of a second process, 

 which begins even in the second month. For there is formed at the 

 place where HUNTER'S ligament traverses the wall of the abdomen 

 an evagination of the peritoneum, the processus vaginalis peritonei 



