372 THE ANATOMY OF THE HORSE. 



Strdctdbe and Interior op the Vagina. The tube of the vagina 

 is about nine or ten inches in length. Posteriorly it joins the vulva, 

 and anteriorly it embraces the cervix uteri. The connection between 

 the cavities of the vagina and uterus is, thus, not by simple continuity, 

 but the vaginal -wall is carried forwards, so as to cause the os uteri to 

 project freely into the forepart of the vaginal canal. 



The wall of the vagina comprises the following layers : — 



1. A Serous Coat. — This is only a partial covering, the posterior part 

 of the organ being without a peritoneal investment. In the hinder part 

 of the tube the place of the peritoneum is taken by connective-tissue 

 uniting it to surrounding parts. This connective-tissue is loose and 

 areolar towards the rectum ; but between the vagina and the bladder it 

 is closer, and forms a more intimate bond between the two organs. 



2. A Muscular Coat. — This is composed of non-striped muscular 

 tissue, continuous in front with the muscular coat of the uterus. 

 Posteriorly the muscular tissue is reddish in tint, and passes into the 

 anterior constrictor of the vulva. The fibres are arranged both longi- 

 tudinally and circularly. 



3. A Mucous Coat. — This lines the tube inwardly, and it is longitudi- 

 nally folded. It possesses numerous mucotis glands, and its epithelium 

 is stratified and squamous. It is of a pinkish, vascular tint, like the 

 mucous lining of the vulva. 



Directions. — Lay open one of the horns of the uterus in its whole 

 extent, and carry the incision along the body and cervix to the os. 



Structure and Interior of the Uterus. The interior of the 

 uterus comprises the cavities of the body and cervix, and those of 

 the horns. 



The Cavity of the Cervix begins posteriorly at the orifice of the tap- 

 like projection already noticed at the forepart of the vaginal canal. This 

 orifice is termed the os uteri externum, or shortly, the os uteri. Ordinarily 

 the orifice is closed, and forms a circular depression from which the folds 

 of mucous membrane radiate outwards, and curve round the circular lip 

 of the OS, to be carried to the vaginal wall. 



In front the canal of the cervix passes gradually into the wider cavity 

 of the body. (In the human subject the connection between the canal 

 of the cervix and the cavity of the body is abrupt, constituting the os 

 uteri internum.) 



The Cavity of the Body is triangular in form, with the base in front. 

 At its posterior angle it passes into the canal of the cervix, and at each 

 antero-lateral angle it is joined by the cavity of a horn. 



The Cavities of the Horns are conical and curved. Each is widest at 

 its base, where it joins the cavity of the body; and it tapers to its 

 anterior extremity, in the centre of which it presents a small tubercle 

 perforated by the uterine orifice of the Fallopian tube. 



