The vagina is a membranous canal, extending from the vulva or _introitus_ to the uterus. It is situated in the cavity of the pelvis, between the bladder in front and the rectum behind; its direction is not in a straight line, but curved from below backwards and upwards. When distended it is cylindrical in shape, but naturally it is flattened from before backwards, so that its walls are ordinarily in contact with each other. In length it averages about four inches in its anterior wall, while its posterior wall describes a segment of a larger circle, that makes it between one and two inches longer. At its commencement it is constricted, and at its upper extremity, where it is attached to the womb, it is dilated, so as to surround the vaginal portion of the neck of the womb (_see_ Plate III, _c_) this is a short distance above the mouth of the womb. The attachment extends higher up on the posterior than on the anterior wall of the womb, which makes the posterior lip of the womb longer than the anterior. The mucous membrane is continuous above with that covering the vaginal portion of the uterus; below it begins at the vulva. Running longitudinally along the anterior and posterior walls are distinct ridges or raphe; these are the columns of the vagina. The relations of the vagina to the neighboring organs can be studied to better advantage by referring to Plate I. [Illustration: PLATE III The Vagina slit open to the neck or Cervix of the Uterus, showing the insertion of the latter into the former. From the author’s own design, beautifully illustrating:— _a._ Fundus (or Base) of the Uterus. _b._ Uterus’ Body. _c._ Cervix, or Neck. _de._ Vaginal part, forming the Anterior and Posterior Lips. _f._ Mouth of the Womb. _gg._ Interior of Vagina, illustrating the Vaginal Folds. _h._ Perineum. _ii._ Round Ligaments. _kk._ Broad Ligaments. _ll._ Uterine Vessels and Nerves. _mm._ Fringed Extremity of the Fallopian Tubes. _nn._ Fallopian Tubes. _oo._ Ovaries.] Its anterior surface is concave, and is in relation with the base of the bladder and with the urethra. Its posterior surface is convex and connected to the anterior wall of the rectum for the lower three-fourths of its extent, the upper fourth being separated from the tube by a fold of the peritoneum, the _recto-uterine fold_, which forms a _cul-de-sac_ between the vagina and rectum. Its sides give attachment superiorily to the broad ligaments, and inferiorily to the Levatores Ani muscles and recto-vesical fascia. THE UTERUS OR WOMB.