2i8 THE UROGENITAL SYSTEM 



Anomalies. — The ovaries vary greatly in form and position. Congenital a:bsence 

 of one or both glands is rare. Cases of supernumerary and bilobed ovaries have been ob- 

 served. 



The Union of the Genital Glands and Mesonephric Tubules. — In both male 

 and female embryos of 21 mm. the mesonephros has degenerated until only 

 twenty-six tubules at most persist, and these are separated into a cranial and a 

 caudal group. In the cranial group of 5 to 12 tubules the collecting portions have 

 separated from the secretory portions. The free ends of these collecting tubules 

 project against that part of the inner epithelial mass which gives rise to the rete 

 tubules of either testis or ovary (Figs. 225 and 227). The cords of the rete de- 

 velop in contact with the collecting tubules of the mesonephros and unite with 

 them. This union was observed by FeHx in fetuses of 60 mm. (C H). In the 

 male, the lumina of rete and collecting tubules become continuous and the latter 

 are transformed into the duduli efferentes of the epididymis. They convey 

 spermatozoa from the testis tubules into the mesonephric duct, which thus 

 becomes the male genital duel. During the fifth month of pregnancy the ductuli 

 efferentes coil at their proximal ends and when surrounded by coimective tissue 

 they are known as lobuli epididymidis. The cranial portion of the male genital 

 duct also coils and forms the ductus epididymidis. Its blind cranial end persists 

 as the appendix epididymidis. 



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

 deferens, extends from the epididymis to the urethra. Near its opening into the 

 latter it dilates to form the ampulla, from the wall of which is evaginated the 

 sacculated seminal vesicle in fetuses of 60 mm. (C H). 



The epithelium of the genital duct is at first a single layer of columnar cells which form 

 non-motile cilia at 70 mm. (C H). Quite late in development the surrounding mesenchyma 

 gives rise to the muscular layers. 



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

 tubules, and the mesonephric duct thus form functional structures (Fig. 238 C). 

 The lower group of collecting tubules persist as the vestigial paradidymis. The 

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

 portion of each degenerates, but the cranial end persists as the appendix testis; 

 the 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 or prostatic utricle. 



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 



