2IO 



THE UROGENITAL SYSTEM 



producing the genital cord (Fig. 232). As the genital glands increase in size they 

 become constricted from the mesonephric fold by lateral and mesial grooves imtil 

 the originally broad base of the genital fold is converted into a stalk (Figs. 225 to 

 227). This stalk-like attachment extends lengthwise and forms in the male the 

 mesorchium, in the female the mesovarium. The urogenital fold is, at the same 

 time, constricted from the dorsal body wall until it is attached only by a narrow 

 mesentery which eventually forms either the ligamentum testis or lig. ovarii. 



The Indifferent Stage of the Genital Ducts. — The mesonephric ducts, with 

 the degeneration of the mesonephroi, become the male genital ducts. In both 



,1 



Lateral hndy 



MiiUerian groove 



vall- 





i^'^M^^' 





t-".^ ■i .;^ '; * '"^ ^..'^ - Mesentery 



w^ 



Mesonephric tubule 



Genital gland 



Anlage of MiiUerian duct 



Fig. 222. — Transverse sections through the anlage of the right MiiUerian duct from a 10 mm. 

 human embryo. X 250. ^, showing the groove in the urogenital epitheliurn; i3, three sections caudad 

 showing the tubular anlage of the duct. 



sexes there also develop a pair of female ducts (of Miiller). In embryos of 10 

 mm. the MiiUerian ducts develop as ventro-lateral thickenings of the urogenital 

 epithelium at the level of the third thoracic segment and near the cranial ends 

 of the mesonephroi. Next, a ventro-lateral groove appears in the epitheKum 

 of the mesonephric fold (Fig. 222 A). Caudally, the dorsal and ventral lips of 

 the groove close and form a tube which separates from, and lies beneath, the 

 epitheKum (Fig. 222 B). Cranially, the tube remains open as the funnel-shaped 

 ostium abdominale of the MiiUerian duct. The solid end of the tube grows 

 caudalwajrd beneath the epithelium, lateral to the mesonephric or male ducts 

 (Figs. 223 to 225). Eventually, by way of the genital cord, the MiiUerian 



