832 GENERATION. 



is not known that its muscular structure takes any part, by contractile action, 

 in the descent of the testicle in the human subject. The epididymis and 

 the vas deferens are formed from the Wolffian body and the Wolffian duct. 



At about the end of the seventh month the testicle has reached the in- 

 ternal abdominal ring ; and at this time a double tubular process of perito- 

 neum, covered with a few fibres from the lower portion of the internal oblique 

 muscle of the abdomen, gradually extends into the scrotum. The testicle 

 descends, following this process of peritoneum, which latter become eventu- 

 ally the visceral and parietal portions of the tunica vaginalis. The canal of 

 communication between the abdominal cavity and the cavity of the scrotum 

 is finally closed, and the tunica vaginalis is separated from the peritoneum. 

 The fibres derived from the internal oblique constitute the cremaster muscle. 



At the eighth or the ninth month the testicles have reached the external 

 abdominal ring and then soon descend into the scrotum. The vas deferens 

 passes from the testicle, along the base of the bladder, to open into the pros- 

 tatic portion of the urethra ; and as development advances, two sacculated 

 diverticula from these tubes make their appearance, which are attached to 

 the bladder and constitute the vesiculae seminales. 



As the ovaries descend to their permanent situation in the pelvic cavity, 

 there appears, attached to the inner extremity of each, a rounded cord, analo- 

 gous to the gubernaculum testis. A portion of this, connecting the ovary 

 with the uterus, constitutes the ligament of the ovary ; and the inferior por- 

 tion forms the round ligament of the uterus, which passes through the in- 

 guinal canal and is attached to the symphysis pubis. 



Development of the Urinary Apparatus. Behind the Wolffian bodies, 

 and developed entirely independently of them, the kidneys, suprarenal cap- 

 sules and ureters make their appearance. The kidneys are developed in the 

 form of little, rounded bodies, composed of short, blind tubes, all converging 

 toward a single point, which is the hilum. These tubes increase in length, 

 branch, become convoluted in a certain portion of their extent, and they 

 finally assume the structure and arrangement of the renal tubules, with their 

 Malpighian bodies, blood-vessels etc. They all open into the hilum. At the 

 time that the kidneys are undergoing development the suprarenal capsules 

 are formed at their superior extremities. These bodies, the uses of which are 

 unknown, are relatively so much larger in the foetus than in the adult that 

 they have been supposed to be peculiarly important in intrauterine life, 

 though nothing definite is known upon this point. The kidneys are rela- 

 tively very large in the foetus. Their proportion to the weight of the body, 

 in the foetus, is 1 to 80, and in the adult, 1 to 240. The ureters undoubtedly 

 are developed as tubular processes from the kidneys, which finally extend to 

 open into the bladder. This fact is shown by certain cases of malformation, 

 in which the ureters do not reach the bladder, but terminate in blind ex- 

 tremities. The development of the genito-urinary apparatus can be readily 

 understood, after the discription just given, by a study of Fig. 312. 



Development of the External Organs of Generation. The external organs 

 of generation begin to be developed at about the fifth week. At the infe- 



