416 DEVELOPMENT OF ORGANS IN MAMMALIA. [CHAP. 



tary tract becomes partially constricted off from the 

 ventral, which then forms a urinogenital sinus (Fig. 140 

 ug). In the course of development the urinogenital 



Fio. 140. 



Diagram of the UniNoaENiTAL Organs of a Mammal at 

 AN Early Stage. (After Allen Thomson ; from Quain's 

 Anatomy.) 

 The parts are seen chiefly in profile, but the MuUerian and 



Wolfl&an ducts are seen from the front. 



3. ureter; 4. urinary bladder; 5. urachus ; ot. genital ridge 

 (ovary or testis); W. left WoMan body; ic. part at apex 

 from which coni vasculosi are afterwards developed ; w. 

 Wolffian duct ; m. Miillerian duct ; go. genital cord consist- 

 ing of Wolffian and Miillerian ducts bound up in a common 

 sheath ; i. rectum ; ug. urinogenital sinus ; cp. elevation 

 which becomes the clitoris or penis ; Is. ridge from which the 

 labia majora or scrotum are developed. 



