_Vagina._—The vagina is a musculo-membranous tube, extending from the vulva to the uterus. The lumen is only virtual, i. e., at rest the vaginal walls are in contact with each other, and the passage appears as a fissure, the latter assuming on a crosscut the form of the letter “H.” The walls of the vagina are composed of three coats, an exterior connective tissue coat, a thick muscular coat and a mucous membrane. The muscular coat comprises two layers of strong unstriped muscular fibres, the outer longitudinal, the inner circular. The latter, being more largely developed near the vaginal aperture, forms a part of the sphincter vaginae. The mucous membrane is covered with a pavement epithelium and is equipped with a great number of papillae, but is devoid of glands. The entire vagina is surrounded by a strong net of venous blood-vessels. The anterior vaginal wall is about seven centimeters long and presents at the mucous surface a median longitudinal ridge; the posterior wall is about ten centimeters long and has two ridges, from which a number of transverse rugae pass, the columnae rugarum. Only a small part of the posterior vaginal wall is in contact with the floor of the pelvis and is covered with peritoneum. The entire vaginal tube lies between the bladder and the rectum. [Illustration: CUT XVII. _Diagram of the pelvic organs._ 1, labia majora; 2, nympha; 3, clitoris; 4, symphysis; 5, urethra; 6, bladder; 7, vagina with columna rugarum; 8, orificium utero-vaginale; 9, internal os; 10, body of uterus; 11, perineum; 12, anus; 13, rectum; 14, peritoneum; 15, vertebra.] [Illustration: CUT XVIII. _Diagram of the uterus._ 1, fundus; 2, cavum uteri; 3, body; 4, internal os; 5, cervix; 6, external os.] “Inter faeces et urinas nascimur” laments the pious father of the Church. A part of the musculus constrictor ani surrounds the orifice of the vagina and is known under the name of constrictor cunni. When the woman is in an erect position, the vaginal orifice looks directly to the ground, the course of the vagina being almost vertical, with a slight inclination from the front to the back toward the vaginal vaults. The vault or fornix is divided by the projecting cervix into two lateral vaults, an anterior shallow and a posterior deep vault. [Illustration: CUT XIX. _Uterus of a four-year-old child._ ce, cylindrical epithelium; mt, muscular tissue; g, uterine gland.]