EXCRETORY ORGANS. 727 



urinogenital opening ; and on each side a genital fold (&). In 

 the male the sides of the groove on the prominence coalesce 

 together, embracing between them the opening of the urino- 

 genital cloaca ; and the prominence itself gives rise to the penis, 



FIG. 407. DIAGRAM OF THE URINOGENITAL ORGANS OF A MAMMAL AT AN 

 EARLY STAGE. (After Allen Thomson ; from Quain's Anatomy.) 



The parts are seen chiefly in profile, but the Miillerian and Wolffian ducts are 

 seen from the front. 



3. ureter; 4. urinary bladder ; 5. urachus; of. genital ridge (ovary or testis) ; W. 

 left Wolffian body ; x. part at apex from which coni vasculosi are afterwards 

 developed ; w. Wolffian duct ; m. Miillerian duct ; gc. genital cord consisting of 

 Wolffian and Mullerian ducts bound up in a common sheath ; i. rectum ; ug. urino- 

 genital sinus ; cp. elevation which becomes the clitoris or penis ; Is. ridge from 

 which the labia majora or scrotum are developed. 



along which the common urinogenital passage is continued. 

 The two genital folds unite from behind forwards to form the 

 scrotum. 



In the female the groove on the genital prominence gradually 

 disappears, and the prominence remains as the clitoris, which is 

 therefore the homologue of the penis : the two genital folds form 

 the labia majora. The urethra and vagina open independently 

 into the common urinogenital sinus. 



