226 UROGENITAL SYSTEM 



The caudal portion of the male duct remains straight and as the ductus def- 

 erens extends from the epididymis to the urethra. Near its opening into the 

 latter it dilates to form the ampulla and from its wall is evaginated the sacculated 

 seminal vesicle in embryos of 60 mm. 



The epithelium of the genital duct is at first a single layer of cubical cells. At 70 mm. 

 the cells become columnar with non-motile cilia at their free ends. Quite late in development 

 the surrounding mesenchyma gives rise to the muscular layers. 



In the male, the rete testis, cranial group of mesonephric collecting tubules 

 and mesonephric duct thus form functional structures (Fig. 231 C). The lower 

 ■ group of collecting tubules persist as the vestigial paradidymis. The Muellerian 

 ducts of male embryos begin to retrograde at 30 mm. The middle portion of each 

 degenerates but its cranial end persists as the appendix testis; its caudal end united 

 with its fellow forms a pouch in the median dorsal wall of the urethra. This is 

 the homologue of the vagina of the female and is called the vagina masculina. 



In the female, the rete ovarii is always a rudimentary structure, yet some 

 time before birth it unites with the cranially persisting group of mesonephric 

 tubules and forms a rudimentary structure, the epoophoron (Fig. 231 B). In its 

 cords lumina appear, the epithelial cells become ciliated and smooth muscle 

 tissue is developed corresponding to that of the epididymis. Usually the greater 

 part of the male genital ducts atrophy in the female, the process beginning at 30 

 mm. Thus the tubules of the epoophoron are without an outlet. The caudal 

 portions of the male genital ducts persist as Gartner's canals. 



These may extend as vestigial structures from the epoophoron to the lateral walls of the 

 vagina, passing through the broad ligament and the wall of the uterus. They open into the 

 vagina close to the free border of the hymen (R. Meyer). The canals are rarely present through- 

 out their entire length and are absent in two-thirds to three-quarters of the cases examined. 

 It is an interesting fact that in male and female embryos the ducts of the opposite sex begin 

 to degenerate at the same stage, 30 mm. 



The Uterine Tubes, Uterus and Vagina. — The Muellerian, or female ducts, 

 after taking their origin as described on p. 218, grow caudally, following the course 

 of the mesonephric ducts (Fig. 217). At first lateral in position, the Muellerian 

 ducts cross the mesonephric ducts and enter the genital cord median to them. 

 In embryos of 20 to 30 mm. their caudal ends are dorsal to the urogenital sinus, 

 extending as far as the Muellerian tubercle, a projection into the median dorsal 

 wall of the vesico-urethral anlage (Fig. 212). This tubercle marks also the posi- 

 tion of the future hymen. In embryos of 70 mm. the Muellerian ducts break 

 through the wall of the urethra and open into its cavity. Before this takes place 



