924 EMBRYOLOGY. 



into the scrotum. The mechanism of this descent has been already 

 explained. 



(It may be only necessary here to state, that in the Equine species the 

 testicles do not usually descend into the scrotum until some time after 

 birth about six months ; while in other animals they reach that sac during 

 foetal life. In the Bovine species, the testes are in the scrotum about the 

 twentieth week of gestation, and in the Sheep and Goat about the fifteenth 

 week; indeed, it has been observed that in all Ruminants their descent is 

 effected before the skin is covered with hair. In the Carnivora, they are 

 usually in the scrotum a few days before birth.) 



Development of the internal genital organs of the female. The ovary is 

 derived from the genital gland, whose anatomical elements are so disposed 

 as to form the stroma, Graafian follicles, and ovules. The Fallopian tube 

 and its pavilion are formed by the anterior part of Miiller's duct, whose 

 extremity shows a small linear orifice. The uterus and vagina arise from 

 the posterior part of Miiller's ducts. These lie beside each other, and end 

 by joining behind to constitute a single canal; this fusion giving origin 

 to the body of the uterus and the vagina. 



The two diverging portions of the ducts comprised between the point of 

 junction and the Fallopian tubes, compose the cornua of the uterus. 



The uterus and vagina are at first placed end to end, without any 

 apparent 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 transverse septum that divides the cloaca into two 

 compartments : the anal opening, and the uro-genital canal. At the inferior 

 end of the latter appears the genital tubercle, a rudiment of the penis or 

 clitoris, and which is surrounded by cutaneous folds the genital folds. 

 This tubercle increases in volume, and has a furrow passing from behind 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, the extremity of which enlarges to constitute the glans. The 

 genital furrow closes posteriorly, and forms the urethra. The folds draw 

 round to each other below the penis, unite in the middle line, and thus 

 produce the scrotum. Owing to these modifications, the digestive ap- 

 paratus is completely separated from the geni to-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 vulvular 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 

 perineum; 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. 



