1052 EMBRYOLOGY. 



separation ; but towards the sixth month the neck of the uterus commences to 

 be defined. 



2. Indifferent state of the external genital organs. — The intestine is terminated 

 by the cloaca — a cavity into which the digestive canal and bladder open by the 

 uro-genital sinus. This confusion quickly ceases by the development of a trans- 

 verse septum that divides the cloaca into two compartments — the anal opening 

 and the uro-genital aperture. At the inferior end of the latter appears the genital 

 tubercle — the rudiment of the penis or clitoris, and wliich is surrounded by 

 cutaneous folds — the genital folds. This tubercle increases in volume, and has 

 a furrow passing from betind to before. Up to this moment it is impossible to 

 distinguish the sexes. 



Development of the external genital organs of the male. — The male sex is marked 

 by the rapid development of the genital tubercle, which becomes the penis — its 

 extremity enlarging to constitute the glans. The genital furrow closes posteriorly, 

 and forms the urethra. The genital folds draw towards each other below the 

 penis, unite in the middle line, and thus produce the scrotum. Owing to these 

 modifications, the digestive apparatus is completely separated from the genito- 

 urinary organs, and the urethral canal is connected with the bladder and the 

 excretory ducts of the testicle. 



Development of the external genital organs of the female. — The indifferent state 

 of the genital organs is readily succeeded by the feminine type. The uro-genital 

 sinus forms the vulvar cavity or vestibulum of the vagina, which is so marked 

 in the lower animals. The genital tubercle becomes the clitoris ; the genital 

 furrow closes at a certain part to constitute the perinasum ; while the genital 

 folds form the labia of the vulva. The mammae — dependencies of the generative 

 organs— appear after the first month of uterine life. 



