DEVELOPMENT OF THE URINARY AND GENERATIVE ORGANS 1211 



antero-lateral abdominal wall. The testis thus acquires an indirect connection 

 with the anterior abdominal wall; and at the same time a portion of the peri- 

 toneal cavity lateral to these fused folds is marked off as the future saccus vagi- 

 nalis. In the inguinal crest a peculiar structure, the gubernaculum testis, makes 

 its appearance. This is at first a slender band, extending from that part of the 

 skin of the groin which afterward forms the scrotum through the inguinal 

 canal to the body and epididymis of the testis. As development advances, the 

 peritoneum enclosing the gubernaculum forms two folds, one above the testis 

 and the other below it. The one above the testis is the plica vascularis, and con- 

 tains ultimately the internal spermatic vessels; the one below, the plica guber- 

 natrix, contains the lower part of the gubernaculum, which has now grown into 

 a thick cord; it ends below at the abdominal inguinal ring in a tube of peritoneum, 

 the saccus vaginalis, which protrudes itself down the inguinal canal. By the fifth 

 month the lower part of the gubernaculum has become a thick cord, while the 

 upper part has disappeared. The lower part now consists of a central core of 

 unstriped muscle fiber, and outside this of a firm layer of striped elements, con- 

 nected, behind the peritoneum, with the abdominal wall. As the scrotum develops, 

 the main portion of the lower end of the gubernaculum is carried, with the skin 

 to which it is attached, to the bottom of this pouch; other bands are carried to 

 the medial side of the thigh and to the perineum. The tube of peritoneum con- 

 stituting the saccus vaginalis projects itself downward into the inguinal canal, 

 and emerges at the cutaneous inguinal ring, pushing before it a part of the Obliquus 

 internus and the aponeurosis of the Obliquus externus, which form respectively 

 the Cremaster muscle and the intercrural fascia. It forms a gradually elongating 

 pouch, which eventually reaches the bottom of the scrotum, and behind this pouch 

 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 certain also that the guber- 

 nacular cord becomes shortened as development proceeds, and this assists in caus^ 

 ing the testis to reach the bottom of the scrotum. By the end of the eighth month 

 the testis has reached the scrotum, preceded by the saccus vaginalis, which com- 

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

 the upper part of the saccus vaginalis usually becomes closed, and this obliteration 

 extends gradually downward to within a short distance of the testis. The process 

 of peritoneum surrounding the testis is now entirely cut off from the general peri- 

 toneal cavity and constitutes the tunica vaginalis. 



Descent of the Ovaries. 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. The gubernaculum in the female lies in contact 

 with the fundus of the uterus and contracts adhesions to this organ, and thus 

 the ovary is prevented from descending below this level. The part of the guber- 

 naculum between the ovary and the uterus becomes ultimately the proper ligament 

 of the ovary, while the part between the uterus and the labium majus forms the 

 round ligament of the uterus. A pouch of peritoneum analogous to the saccus 

 vaginalis in the male accompanies it along the inguinal canal: it is called the canal 

 of Nuck. In rare cases the gubernaculum may fail to contract adhesions to the 

 uterus, and then the ovary descends through the inguinal canal into the labium 

 majus, and under these circumstances its position resembles that of the testis. 



The Metanephros and the Permanent Kidney. The rudiments of the perma- 

 nent kidneys make their appearance about the end of the first or the beginning 

 of the second month. Each kidney has a two-fold origin, part arising from the 

 metanephros, and part as a diverticulum from the hind-end of the Wolffian duct, 



