THORAX AND ABDOMEN OF THE HORSE 185 



cm, in length. Its dorsal wall is in contact with the rectum, with which 

 it is connected by loose fibrous tissue. Its ventral wall rests on the 

 floor of the pelvis ; while laterally the vestibule is covered by the 

 levator ani muscle. 



A constrictor muscle (m. constrictor vestibuli) covers the ventral 

 and lateral walls of the vestibule, some of the fibres of the muscle 

 becoming lost on the wall of the rectum. 



Vulva} — No sharp line of demarcation distinguishes the vestibule 

 from the vulva, the external opening of which (rima pudendi) is a 

 vertical elongated slit with dorsal and ventral comnvissures (commissura 

 dorsalis : commissura ventralis), of which the ventral is the more 

 rounded. The margins of the opening are formed by the prominent 

 and rounded labia pudendi. 



Immediately within the ventral commissure of the vulva is the 

 clitoris, the homologue of the penis of the male. The rounded free 

 end of the clitoris is the glans (glans clitoridis). The body (corpus 

 clitoridis) is formed by two corpora cavernosa clitoridis which diverge 

 to form the crura (crura clitoridis) attached to the sciatic arch. The 

 glans of the clitoris reposes in a fossa clitoridis, and is provided with a 

 small fold of membrane, the prepuce of the clitoris (prseputium 

 clitoridis). 



A very small and inconspicuous ischio-cavernous muscle arises from 

 the ischium and ends on the clitoris. A constrictor muscle of the 

 vulva (m. constrictor vulvae) lies between the skin and the mucous 

 membrane and is connected with the external sphincter of the anus. 

 This, with the constrictor of the vestibule, may be regarded as the 

 homologue of the bulbo-cavernous muscle of the male. 



Vestibidar bulbs (bulbi vestibuli). — If the constrictor muscle of the 

 vestibule be removed, an elongated mass of erectile tissue will be 

 exposed on each side. These are the vestibular bulbs, which correspond 

 to the bulb of the urethra of the male. Blood is carried to each bulb 

 by a large branch of the internal pudendal artery. 



A. PUDENDA INTERNA. — The internal pudendal artery has the same 

 general course and disposition as in the male ; but differences in the 

 female pelvic organs necessitate peculiarities of distribution. The vessel 

 ends by dividing into the perineal artery (a. perinei) and the artery of 

 the clitoris (a. clitoridis). The middle hsemorrhoidal artery is larger 

 than that of the male, and furnishes a caudal uterine artery (a. uterina 

 caudalis), which supplies the vagina and the body of the uterus, and 



^ Vulva [L.], a wrapper or covering. The word vulva or volva seems to have 

 been originally applied to the uterus. Horace is said to have used volva when 

 referring to the uterus of the pig as a favourite dish. 



