TRANSFORMATION OF THE MESONEPHRIC TUBULES AND DUCTS 2IQ 



Transformation of the Mesonephric Tubules and Ducts. 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 develop in contact with the 

 collecting tubules of the mesonephros and unite with them in fetuses of 

 60 mm. (C H). 



In the male, the lumina of rete and collecting tubules become contin- 

 uous and the cranial group of the latter are transformed into the ductuli 

 ejrferentes of the epididymis. During the fifth month of pregnancy the 

 ductuli efferentes coil at their proximal ends, and when surrounded by 

 connective tissue they are known as lobuli epididymidis. The lower 

 group of collecting tubules persist as the vesitigial paradidymis and 

 ductuli abber antes (Fig. 238 C}. 



The efferent ductules convey spermatozoa from the testis tubules 

 into the mesonephric duct, which thus becomes the male genital duct. 

 The cranial portion of the mesonephric duct 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 mesen- 

 chyma gives rise to the muscular layers. 



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

 some time before birth it becomes tubular and unites with the cranial 

 persisting group of mesonephric collecting tubules which forms a rudi- 

 mentary structure, the epoophoron (Fig. 238 B}. The epithelial cells of 

 the latter become ciliated, and smooth muscle tissue is developed corres- 

 ponding to that of the epididymis. The caudal group of mesonephric 

 tubules constitute the paroophoron. 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 left without an outlet. Portions 

 of the mesonephric ducts persist as (Gartner's) ducts of the epoophoron. 



Gartner's ducts may extend as vestigial structures from these 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 ducts are 

 rarely present throughout their entire length and are absent in two-thirds to three-quarters 

 of the cases examined. 



