422 TEXT-BOOK OF EMBRYOLOGY. 



Since the testicle is invested by peritoneum from the beginning of its develop- 

 ment, it must be understood that in its passage into the scrotum it passes along 

 under the peritoneum. Consequently when it reaches the scrotum it is sur- 

 rounded by a double layer of peritoneum, the tunica vaginalis propria. 



The descent of the testicle also produces marked changes in the course of 

 the deferent duct. Primarily the (mesonephric) duct extends cranially from 

 the urogenital sinus in a longitudinal direction. But as the testicle migrates, 

 the cephalic end of the duct is drawn caudally so that in the adult the deferent 

 duct extends cranially from the scrotum to the ventral side of the urinary 

 bladder and then bends caudally again to open into the urethra. 



Descent of the Ovaries. The ovaries undergo a change of position cor- 

 responding to the descent of the testicles, although the change is not so extensive. 

 Primarily the Miillerian and mesonephric ducts lie in a ridge on the surface of 

 the mesonephros (p. 413). As the mesonephros and its duct atrophy, the Miil- 

 lerian duct (oviduct) comes to lie in a fold, the mesosalpinx, which is attached 

 to the mesovarium (Fig. 373) . At the same time the mesovarium becomes directly 

 continuous with and really a part of the inguinal ligament. The latter cor- 

 responds, of course, to the gubernaculum testis, and plays a role in the descent 

 of the ovaries. It may be conveniently divided into three parts, (i) a cephalic 

 part which is attached to the hilus of the ovary, (2) a middle part which ex- 

 tends from the ovary to the uterus, forming the ovarian ligament, and (3) a cau- 

 dal part which extends from the uterus to the inguinal region, forming the 

 round ligament of the uterus (Fig. 377). The round ligament pierces the body 

 wall and is attached to the corium of the skin. At the point where it passes 

 through the body wall there is a slight evagination of the peritoneum, the 

 diverticulum of Nuck, which corresponds to the processus vaginalis peritonei 

 in the male. 



The ovaries gradually migrate caudally from their original position into the 

 false pelvis (third month) and thence into the true pelvis (at birth). Obviously 

 no traction can be exerted upon them by the round ligament (or caudal part of 

 the inguinal ligament), since the latter extends from the uterus to the inguinal 

 region. Their descent into the pelvic seems to be due to the unequal growth 

 of the ovarian ligaments, or in other words, to the fact that the ovarian liga- 

 ments grow proportionally less than the surrounding parts. During their 

 descent the ovaries become embedded in the broad ligaments of the uterus, 

 which represent further development of the peritoneal folds of the genital cord. 

 In this way the mesovarium becomes merged with the broad ligament. 



On pages 420 and 421 are three diagrammatic representations of the changes 

 that take place in the genital systems of the two sexes. Fig. 378 represents 

 the " indifferent " stage in which all the embryonic structures are present; 

 Fig. 379 represents the changes that occur in the male; Fig. 380 represents the 



