3 1 8 Vertebrate Embryology 



genital tubercle or clitero-penis (Figs. 106-1 1 7). 

 The end of this tubercle soon shows a slight 

 enlargement, the glans. Along the posterior 

 part of the ventral side of the tubercle is a 

 groove, the genital groove or uro-genital sinus, 

 whose edges are thickened to form \h& genital 

 folds. Lateral to these folds are two others 

 of greater extent, the genital swellings. This 

 condition is reached at about the tenth week 

 of foetal life and is the same in both sexes ; or, 

 in other words, the external genitalia do not 

 begin to show sexual differentiation until about 

 the tenth week. 



In the female the genital tubercle remains 

 small and becomes the clitoris. The genital 

 groove remains open as the vestibule, the gen- 

 ital folds becoming the labia minora, and the 

 genital swellings the labia majora. 



In the male the genital tubercle continues 

 to increase in size and becomes the penis. 

 The genital groove normally closes to be- 

 come the penial urethra. The genital folds 

 become the prepuce. The genital swellings 

 fold over to become the scrotum, into which 

 the testes later descend (about the eighth or 

 ninth month) from their early position in the 

 body-cavity. 



