DEVELOPMENT OF URINARY AND GENERATIVE ORGANS 1427 



pushing before it a part of tne Internal oblique and the aponeurosi,s of the External oblique, 

 which form, respectively, the Cremaster muscle and the external spermatic fascia. It forms a 

 gradually elongating pouch or cul-de-sac, which eventually reaches the bottom of the scrotum, 

 and behind this the testis is drawn by the growth of the body of the fetus, for the gubernaculum 

 does not grow commensurately with the growth of other parts, and therefore the testis, being 

 attached by the gubernaculum to the bottom of the scrotum, is prevented from rising as the body 

 grows, and is drawn first into the inguinal canal and eventually into the scrotum. It seems cer- 

 tain also that the gubernacular cord becomes shortened as development proceeds, and this assists 

 in causing the testis to reach the bottom of the scrotum. By the eighth month the testis has 

 reached the scrotum, preceded by the lengthened pouch of peritoneum, the processus vaginalis, 

 which communicates by its upper extremity with the peritoneal cavity. Just before birth the 

 upper part of the pouch usually becomes closed, and this obliteration extends gradually down- 

 ward to within a short distance of the testis. The process of peritoneum surrounding the testis 

 is now entirely cut off from the general peritoneal cavity and constitutes the tunica vaginal i ft. 1 



In the female there is also a gubernaculum, which effects a considerable change in the position 

 of the ovary, though not so extensive a change as in that of the testis in the male. The guber- 

 naculum in the female, as it lies on either side in contact with the fundus of the uterus, contracts 

 adhesions to this organ, and thus the ovary is prevented from descending below this level. The 



Miillerian 



duct. 



Allantois. \KMney diverticulum. 

 Umbilical cord, \ \Rectum.^ 



Umbilical vessels. 



Hindgut. 



Noiochord. 



FIG. 1186. Tail end of human embryo of twenty- 

 five to twenty-nine days old. (From model by 

 Keibel.) 



FIG. 1187. Tail end of human embryo of thirty- 

 two to thirty-three days old. (From model by 

 Keibel.) 



upper part of the gubernaculum, i. e., the part between the ovary and the uterus, becomes ulti- 

 mately the rounded ligament of the ovary, while the lower part, i. e., the part between the attach- 

 ment of the cord to the uterus and its termination in the labius majum, ultimately forms the round 

 ligament of the uterus. A pouch of peritoneum accompanies it along the inguinal canal, analogous 

 to the processus vaginalis in the male; it is called the canal of Nuck. In rare cases the guber- 

 naculum may fail to contract adhesions to the uterus, and then the ovary descends through the 

 inguinal canal into the labium majus, extending down the canal of Nuck, and under these 

 circumstances its position resembles that of the testis in the male. 



The Metanephos or Permanent Kidney. The rudiments of the permanent kidneys make 

 their appearance about the end of the first or beginning of the second month. Each arises as a 

 diverticulum from the hind end of the Wolffian duct, close to where the latter opens into the 

 cloaca (Figs. 1186, 1187). This diverticulum grows upward and forward into the posterior 

 part of the intermediate cell mass, where its blind or anterior extremity becomes dilated and sub- 

 sequently divides into several buds, which form the rudiments of the pelvis and calyces of the 

 ureter. By further subdivisions it gives rise to the collecting tubules of the kidney. The 

 secretory tubules are developed from condensations of the nephrogenic tissue. At first these 

 are spherical masses of cells which become hollowed, forming the renal vesicles. These become 

 elongated and S-shaped; one end of the S-shaped tube becomes continuous with the lumen of 

 a renal diverticular branch, the other end becomes cup-shaped and then spherical, being invagi- 

 nated by a tuft of capillaries derived from the' renal artery to form a glomerulus. The inter- 

 vening portions of the tube become convoluted and looped to form the uriniferous tubule. The 

 mesoderm around the subdivisions of the diverticulum becomes condensed to form the connec- 

 tive tissue and vessels of the kidney. The diverticulum is elongated to form the ureter, the 

 posterior extremity of which opens at first into the hind end of the Wolffian duct; after the 

 sixth week it separates from the Wolffian duct, and opens independently into the part of the 



i The obliteration of the process of peritoneum which accompanies the cord, and is hence called the funicular 

 process, is often incomplete. 



