ANATOMICAL FEATURES 11 



volved in such movements are still unknown, and the study of such behavior 

 forms one of the many interesting aspects of embryological investigation 

 awaiting solution. 



Various theoretical explanations have been proposed, however, to explain 

 the movement of the testis posteriad from its original embryonic site. Classical 

 theory mentions the mechanical pull or tightening stress of the gubernaculum, 

 a structure which develops in relation to the primitive genital fold or genital 

 ridge (figs. 3B, C; 351C-7). 



The genital ridge extends along the mesial aspect of the early developing 

 mesonephric kidney from a point just caudal to the heart to the posterior 

 extremity of the mesonephric kidney near the developing cloacal structures 

 (Hill, '07). Anteriorly, the genital ridge (fold) merges with the diaphragmatic 

 ligament of the mesonephros (fig. 3A). The gonad (testis or ovary) develops 

 in a specialized region of the more cephalic portion of the genital ridge 

 (Allen, '04). (See fig. 3A.) The caudal end of the mesonephric kidney even- 

 tually becomes attached to the posterior ventral body wall by means of a 

 secondary formation of another cord of tissue, the inguinal fold (fig. 3A). 

 The latter is attached to the posterior ventral body wall near the area where 

 the scrotal outpushing (evagination) later occurs. This inguinal fold later 

 becomes continuous with the genital fold (fig. 3B). The inguinal fold thus 

 becomes converted into a ligament, the inguinal ligament of the mesonephros, 

 uniting the caudal portion of the mesonephric kidney and adjacent genital 

 fold tissue with the area of scrotal evagination (fig. 3B). The gubernaculum 

 represents a later musculo-connective tissue development of the inguinal liga- 

 ment and the adjacent genital fold tissue. It contains smooth muscle fibers 

 as well as connective tissue. As the scrotal evagination forms at the point 

 where the gubernaculum attaches to the body wall, the gubernaculum from 

 the beginning of its formation is connected with the developing scrotal sac. 



As the testis migrates posteriad, the anterior suspensory ligament of the 

 testis elongates and the gubernaculum shortens (fig. 3A-F). This decrease 

 in length of the gubernaculum is both real and relative. It is real in that an 

 actual shortening occurs; it is relative because the rapid enlargement of the 

 developing pelvic cavity and its contained organs makes the length of the 

 gubernaculum appear less extensive. This enlargement of the pelvic space 

 and increase in size of its contained structures and a corresponding failure 

 of the gubernaculum to elongate, certainly are factors in bringing about the 

 intra-abdominal descent of the testis; that is, testis descent within the peritoneal 

 cavity itself (Felix, '12). 



Developmental preparations precede the extra-abdominal descent of the 

 testes, for the scrotal chambers must be prepared in advance of the arrival 

 of the testes. These developmental events are: 



( I ) two outpocketings of the abdominal wall which come to lie side by 

 side below the skin to form the walls of the scrotal chamber, and 



