410 EMBRYOLOGY. 



37. The term cloaca is applied to a depression at the hinder end of 

 the embryo, into which open the hind gut and the allantois, after 

 the latter has received on the posterior face of its attenuated 

 terminal part, the sinus urogenitalis the closely approximated 

 Miillerian and mesonephric ducts. 



38. The cloaca becomes divided by projecting folds, which unite 

 to form the perinseum, into an anterior [ventral] and posterior 

 [dorsal] portion, of which the former is the prolongation of the 

 sinus urogenitalis, the latter the prolongation of the intestine 

 (anus). 



39. At the anterior margin of the cloaca, or, after completed 

 separation, at the anterior rim of the sinus urogenitalis, there is 

 found in both sexes the genital eminence, which bears along its 

 under surface a groove flanked by the two genital folds ; the eminence, 

 together with the opening lying under it (cloaca or sinus urogeni- 

 talis), is embraced by the genital ridges. 



40. In the female the genital eminence remains small and becomes 

 the clitoris, the genital folds become the labia minora, the genital 

 ridges the labia majora; the sinus urogenitalis remains short and 

 broad and represents the vestibulum, which receives the vagina (the 

 end of the Miillerian ducts) and the external orifice of the allantois 

 or urinary bladder, the female urethra. 



41. In the male the genital eminence grows out to a great length 

 as the male organ ; the genital folds close on their under surface to 

 form a narrow canal, which appears as a prolongation of the narrow 

 sinus urogenitalis, together with the latter is designated as the 

 male urethra, and receives at its beginning the vas deferens and the 

 uterus masculinus ; the two genital ridges, which increase in size for 

 the reception of the testes, surround the roots of the male organ and 

 unite to form the scrotum. 



42. The following table gives a brief survey (1) of the compar- 

 able parts of the outer and inner sexual organs of the male and 

 female, and (2) of their derivation from indifferent fundaments of 

 the urogenital system in Mammals : 



