THORAX AND ABDOMEN OF THE HORSE 187 



uteri), on which is the puckered external uterine opening ^ (orificiura 

 uteri externum). The interior of the canal of the cervix is occupied by 

 numerous and prominent longitudinal folds (plicae cervicis), which are 

 continued beyond the external uterine opening, and give this opening 

 its characteristic puckered appearance. 



INTERIOR OF THE VAGINA. — The mucoiis lining of the vagina is 

 thrown into low longitudinal folds. Because of the projection of the 

 cervix of the uterus into the vagina, an arch-like continuity of the 

 mucous membrane of the two organs is produced (fornix vaginae). It 

 should be noted that the fornix is formed by that part of the vagina 

 that is covered by peritoneum, so that an incision through the wall of 

 the vagina in the fornix will produce an opening into the peritoneal 

 cavity. 



INTERIOR OF THE VESTIBULE. — On the ventral wall of the vestibule, 

 close to its junction with the vagina proper, is the conspicuous external 

 opening of the urethra (orificium urethrae externum). 



The female urethra (urethra feminina) is a short (5-7 cm.) but wide 

 and very dilatable tube, homologous with that portion of the male 

 urethra that extends from the neck of the bladder to the seminal 

 colliculus. It lies in the middle line ventral to the vagina, with which 

 its caudal moiety is intimately connected. It is surrounded by a 

 urethral muscle, which is continuous with the constrictor of the 

 vestibule, 



A fold of mucous membrane, between the urethral opening and the 

 vagina, and extendinsr for a variable distance on to the lateral wall of 

 the genital passage, is all that can be said to represent a hymen. 



If the wall of the vestibule be examined carefully, two rows of small 

 papillae should be found on each side. The papillae of the dorsal row 

 are the larger, and number from eight to ten. Their summits are 

 pierced by the ducts of the larger vestibular glands (glandulse vesti- 

 bulares majores). The papillae of the ventral row are smaller, and the 

 right and left rows converge towards the ventral commissure of the 

 vulva. The ducts of the lesser vestibular glands (glandule vestibulares 

 minores) open on these papillae. 



Complete the dissection of the female pelvis by an examination of 

 the connection of the hip-bone with the vertebral column (see 

 page 179). 



^ Frequently referred to as the os uteri. 



