VAGINA.
Syn. Vulvo-uterine canal. —The vagina con stitutes a flattened cylindroid, extending from the vulvar orifice to the neck of the uterus. It lies entirely within the pelvis, between the bladder and rectum, running very nearly in the direction of the axis of the pelvic outlet, but having a slight curvature forwards. The orifice of the vagina is bounded anteriorly by the vestibule, laterally by the nymph, and posteriorly by the hymen. The upper or blind extremity, termed the fornix, receives the va ginal portion of the uterine neck, which is not placed exactly at the termination of the canal, but appears as if it were let into its upper wall (fig. 433.).
Dimensions.—The vagina is capable of con siderable extension. It varies in dimensions in different subjects. In the ordinary virgin state, the anterior wall, which is the shorter, measures, from the median tubercle of the vagina to the anterior lip of the uterus, less than two and a half inches ; and the posterior wall, from the centre of the vulvar orifice to the end of the fornix, three inches. The transverse diameter, in the natural state of the canal, which is flattened from before back wards, so that the anterior and posterior walls are in contact, measures ordinarily one inch and a quarter. But when the canal is dis tended, and after the birth of many children, these dimensions may be much exceeded.
External surface.— The fcrllowing are the relations of the external surface of the vagina. Anteriorly,it is connected to the urethra and base of the bladder by arcolar tissue. Laterally, it is in relation with the root of the broad liga ment and the pelvic fascia. Posteriorly, in the first part of its course, it is covered by the pe ritoneum, forming the anterior wall of the retro-uterine pouch, or space of Douglas ; secondly, where the peritoneum ceases, and for about half its course, it is united to the rectum ; and lastly, it is separated from the latter by the thickness of the perineum.
Composition.— The walls of the vagina are of variable thickness in different parts, the average being 1"'. They are composed of three coats. The outermost of these is formed of fibrous tissue, intermixed with an abundance of elastic fibre. Beneath this is a second or muscular coat, containing unstriped muscular fibre and fibre-cells, which, during pregnancy, undergo a development similar to that of the uterine fibre. The third, or innermost, is the mucous coat, composed of a dense connective tissue, with much admixture of elastic fibre, to which is due a great part of that elasticity and distensibility with which the vagina is en dowed. Imbedded in the substance of the mucous membrane, which is covered by squa mous epithelium, are numerous xnuciparous follicles.
Internal surface.—Upon the inner surface of the canal the mucous membrane is thrown into folds, which, in the virgin, form numerous closely-set transverse rugw, that are arranged with a certain approach to regularity, and sometimes exhibit a central connecting line or raphe, forming the columme rugarum, upon the anterior and posterior walls. At the sides
of the vagina these folds are less prominent, and take an oblique or longitudinal direction. In some subjects the rugm are covered by, or are chiefly composed of, short, crowded ver rucose papillx, intermixed with others more filiform. They become larger towards the vaginal orifice, where they sometimes take the form of little leaflets, resembling the smaller fimbrix of the Fallopian tube, especially about the meatus urinarius. After numerous acts of parturition, as well as from frequent inter course, the folds become obliterated, and the inner surface of the vagina is rendered nearly or entirely smooth.
Arteries.—A special artery usually exists for the vagina, which may arise either from the hypogastric, internal pudic, middle hwinor rhoidal, or even from the obturator. From one of these origins the artery descends along each side of the vagina, giving off in its course numerous branches, which inosculate in the recto-vaginal septum with those of the op posite side. Near its extremity, the artery sends off a considerable branch to the bulb of the vagina, and after supplying the external organs, it terminates by inosculating with the artery Of the opposite side, between the vagina and rectum. One or two separate branches are generally found to arise from the uterine artery. These descend between the bladder and the vagina, supplying branches to both those parts. An abundant and intricate net work is formed in the vaginal walls by the ramifications of the smaller vessels derived from these sources, which interpenetrate the several coats down to the mucous membrane.
reins.— The veins which collect the blood from the labia, constrictor muscles, and mu cous membrane of the vagina, and from the erectile tissue forming the vaginal bulb, unite to form a considerable plexus, especially around the vulvar orifice termed the vaginal plexus. From this plexus branches pass to the vesical, and lixmorrhoidal, and uterine plexuses ; the blood being finally collected by large veins which empty themselves into the internal iliacs. Figs. 482. and 4K3.
The Lympatics are those which are common to the bladder, cervix uteri, and lower part of the rectum. They terminate in the pelvic glands.
The Nerves are derived from the pelvic plexus, which contains a large proportion of tubular fibres, derived frorn the fourth and fifth sacral nerves.
Uses of the vagina. — The vagina, dining copulation, serves for the reception of the male intromittent organ, and for the lodge ment of the seminal fluid in such a posi tion as to facilitate the introduction of that fluid into the uterus.* During menstruation the vagina gives passaoe to the catamenia. In labour it transmits t'he fcetus and secun dines, and subsequently the lochia.