362 SPLANCHNOLOGY. 



VULVA. 



This, the external orifice of the urino-genital system, is 

 situated in the perineal region, immediately below the anus ; 

 the opening appears as a long verticle ovoid slit, the fissura 

 magna, presenting two lips and two commissures. The labia, 

 or lips, are formed by an external soft unctuous layer of skin, 

 destitute of hair, but rich in pigment, and an inner one of 

 mucous membrane ; between these is a quantity of fat and 

 areolar tissue, most abundant in the young animal, and the 

 erectile vaginal bulb, divided into two branches, which leave the 

 clitoris, and pass along the sides of the vulva, terminating in 

 round lobes ; this structure is filled with blood during copulation, 

 rendering co-aptation very complete. The superior commissure 

 is very acute, and reaches almost to the anus ; the space between 

 the two is the perinceum. The inferior commissure is obtuse 

 and rounded. 



In the interior of the vulva, and in a depression on its floor, 

 called the fossa navicularis, lies the clitoris, which originates 

 by two crura from the ischial arch, and is attached to the 

 symphysis by a suspensory ligament. The clitoris passes back- 

 wards, jutting towards the inferior commissure, its free extremity 

 being lodged in the fossa navicularis, and enveloped by a mucous 

 covering, the prepuce of the clitoris. The structure of the 

 clitoris resembles that of the corpora cavernosa of the male ; and, 

 having a fibrous capsule, erectile tissue, and cavernous vessels, it 

 becomes erect during copulation. 



The external orifice of the urethra, the meatus urinarius, 

 opens on the inferior surface of the vulva, about four inches from 

 its external opening ; it is larger than the male opening, and 

 surmounted by a fold of mucous membrane, which acts as a 

 valve. The hymen is a thin semilunar fold of mucous membrane, 

 which separates, usually imperfectly, the vulva from the vagina, 

 lying immediately before the meatus ; it is ruptured during the 

 first act of copulation, which gives rise to a number of small 

 round elevations surrounding the entrance of the vagina, called 

 the carunculcB inyrtiformes. 



The mucous membrane lining the vulva is pale rose-coloured, 

 and covered with mucous follicles, which are more numerous near 

 the opening of the urethra, and sebaceous glands, the glandular 



