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3d. 4. The Vagina
The vagina (Fig. 1166) extends from the vestibule to the uterus, and is situated behind the bladder and in front of the rectum; it is directed upward and backward, its axis forming with that of the uterus an angle of over 90°, opening forward. Its walls are ordinarily in contact, and the usual shape of its lower part on transverse section is that of an H, the transverse limb being slightly curved forward or backward, while the lateral limbs are somewhat convex toward the median line; its middle part has the appearance of a transverse slit. Its length is 6 to 7.5 cm. along its anterior wall, and 9 cm. along its posterior wall. It is constricted at its commencement, dilated in the middle, and narrowed near its uterine extremity; it surrounds the vaginal portion of the cervix uteri, a short distance from the external orifice of the uterus, its attachment extending higher up on the posterior than on the anterior wall of the uterus. To the recess behind the cervix the term posterior fornix is applied, while the smaller recesses in front and at the sides are called the anterior and lateral fornices. Relations.—The anterior surface of the vagina is in relation with the fundus of the bladder, and with the urethra. Its posterior surface is separated from the rectum by the rectouterine excavation in its upper fourth, and by the rectovesical fascia in its middle two-fourths; the lower fourth is separated from the anal canal by the perineal body. Its sides are enclosed between the Levatores ani muscles. As the terminal portions of the ureters pass forward and medialward to reach the fundus of the bladder, they run close to the lateral fornices of the vagina, and as they enter the bladder are slightly in front of the anterior fornix. Structure.—The vagina consists of an internal mucous lining and a muscular coat separated by a layer of erectile tissue. The mucous membrane (tunica mucosa) is continuous above with that lining the uterus. Its inner surface presents two longitudinal ridges, one on its anterior and one on its posterior wall. These ridges are called the columns of the vagina and from them numerous transverse ridges or rugæ extend outward on either side. These rugæ are divided by furrows of variable depth, giving to the mucous membrane the appearance of being studded over with conical projections or papillæ; they are most numerous near the orifice of the vagina, especially before parturition. The epithelium covering the mucous membrane is of the stratified squamous variety. The submucous tissue is very loose, and contains numerous large veins which by their anastomoses form a plexus, together with smooth muscular fibers derived from the muscular coat; it is regarded by Gussenbauer as an erectile tissue. It contains a number of mucous crypts, but no true glands. The muscular coat (tunica muscularis) consists of two layers: an external longitudinal, which is by far the stronger, and an internal circular layer. The longitudinal fibers are continuous with the superficial muscular fibers of the uterus. The strongest fasciculi are those attached to the rectovesical fascia on either side. The two layers are not distinctly separable from each other, but are connected by oblique decussating fasciculi, which pass from the one layer to the other. In addition to this, the vagina at its lower end is surrounded by a band of striped muscular fibers, the Bulbocavernosus (see page 430). External to the muscular coat is a layer of connective tissue, containing a large plexus of bloodvessels. The erectile tissue consists of a layer of loose connective tissue, situated between the mucous membrane and the muscular coat; imbedded in it is a plexus of large veins, and numerous bundles of unstriped muscular fibers, derived from the circular muscular layer. The arrangement of the veins is similar to that found in other erectile tissues.
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