226 



THE UROGENITAL SYSTEM 



the right and left labia major a; (3) caudally, the posterior commissure (Fig. 

 236). The glans of the phallus forms the glans clitoridis of the female. 

 On the anal surface of the phallus, beginning at the coronary sulcus, the 

 primitive urogenital opening closes distally, forming the urethral groove. 

 Proximally it remains open, as the definitive urogenital opening near the 

 base of the phallus. The lips of this groove and opening enlarge and 

 become the labia minora. The cranial surface of the phallus forms a fold, 



A B c 



FIG. 236. Three stages in the development of the female external genitalia (after Tour- 

 neux in Heisler). i, Clitoris; 2, glans clitoridis; 3, urogenital aperture on each side of which are 

 the labia minora (7); 4, labia majora; 4, anus; 7, labia minora. 



the prepucium, which, however, is not the exact homologue of the male 

 fore-skin. This in the female is represented by a ring-like rudiment at 

 the base of the glans clitoridis (Felix, 1912). 



Male. The phallus grows rapidly at its base, so that the glans and 

 primitive urogenital opening are carried some distance from the anus (Fig. 

 237). A cylindrical collar of the epithelium, incomplete on the anal side, 

 grows down into the end of the glans, which becomes the glans penis. By 

 the disappearance of the central cells of the epithelial downgrowth, an 

 outer cylindrical mantle, the prepucium, or fore-skin, is formed about the 

 spheroidal glans (cf. Fig. 158). Where the epithelial downgrowth is in- 

 complete the glans and fore-skin remain connected, the persisting connec- 

 tion being the jrenulum prepucii. The corpora cavernosa penis arise as 

 paired mesenchymal columns. The corpus cavernosum urethra results 

 from the linking of similar, unpaired anlages, one in the glans the other 

 in the shaft. 



The urogenital sinus, as we have seen, extends out into the phallus 

 and in the glans becomes the solid urethral plate. With the great elonga- 



