DISSECTION OF THE PELVIS. 371 



vagina is to be exposed by a mesial incision on the upper wall of 

 these organs. 



The Canal of the Vulva, or Vestibule. This, as already stated, is 

 a tubular passage about five inches in length. When removed from 

 the body and inflated it assumes a large calibre, but ordinarily its walls 

 are in contact. Tracing the canal in an order inverse to that followed 

 in the previous description of parts, it may be said to begin on the 

 surface of the body at the vertical slit already described, and to 

 terminate in front by joining the tube of the vagina. In the adult 

 animal there is little or nothing to mark the line of separation between 

 the two passages, the canal of the vulva usually passing without 

 interruption into that of the vagina. 1 The vulva is lined by a 

 mucous membrane of a rosy, vascular tint. It possesses numerous 

 mucous follicles ; and its free surface is formed by a stratified squamous 

 epithelium, which, towards the external opening, is often pigmented in 

 spots. 



The Meatus Urinarius. The urethra opens on the middle line of 

 the floor of the vulva immediately behind its point of continuity with 

 the vagina. The opening is surmounted by a large mucous fold — the 

 valve of the meatus urinarius. This valve has its free edge directed 

 backwards, and it serves to direct the flow of urine towards the exterior. 

 Its presence must be remembered in passing the female catheter, the 

 point of which should be made to press on the floor of the vulva as it 

 is directed onwards. The meatus is of large size when compared with 

 the same orifice in the male, since it readily admits two fingers. 



Directions. — Reverse the natural position of parts, laying the uterus, 

 vagina, and vulva with their upper surfaces downwards, and open the 

 bladder by a mesial incision on its lower (in the natural position) face. 

 For an account of the structure of the bladder turn to page 359. 



The Urethra of the female is very much shorter, but considerably 

 wider, than the corresponding tube of the male. Beginning as a funnel- 

 like prolongation of the neck of the bladder, it passes backwards on the 

 middle line of the lower face of the vagina, in whose wall it is partially 

 imbedded ; and, after a course of two or three inches, it perforates the 

 lower wall of the vulva, and opens by the meatus already described. 

 The calibre of the tube is in correspondence with the large size of the 

 meatus ; and with slight stretching it will accommodate three fingers. 

 The wall of the urethra is composed of connective-tissue, and non- 

 striped muscular fibres circularly disposed ; and it is lined internally 

 by a longitudinally folded mucous membrane with a stratified squamous 

 epithelium. 



1 As a rule, nothing meriting the name of a hymen is present at the junction of the 

 vulva with the vagina, even in virgin mares ; but, as a rare abnormality, an almost or 

 quite complete membranous septum may be developed in this position. 



