_Uterus._—The uterus is a hollow, pyriform, flattened, thick muscular organ. It is divided into the upper thick end, or fundus, the body, and the neck or cervix. The uterine cavity has somewhat the shape of a triangle, its basis corresponding to the uterine base. The uterine cavity communicates with the canals of the Fallopian tubes by two openings at the angles of the basis. The lower angle is continued into the cervical canal and opens into the vagina. The median part of the cervical canal is widened. The narrow opening into the cavity of the uterus is known under the name of os internum, while the opening into the vagina is called os externum. The uterine cavity is coated with a mucous membrane, covered with columnar epithelia of the ciliated type, which bears a great number of tubular glands. The mucous membrane of the cervical canal shows a system of small folds, the arbor vitae. The covering of the cervical canal is also a high columnar, ciliated epithelium. The latter changes into a pavement epithelium at the external os. [Illustration: CUT XX. _Cervix uteri from a day-old infant._ pe, pavement epithelium of the vaginal portion of the cervix; c, border-line of the portio and the cavity of the cervix; CE, cylindrical epithelium of the cavity of the cervix; v, blood-vessels.] The second uterine coat consists of non-striated muscular fibres. The uterus has no submucosa. There is an inner circular and an outer longitudinal muscular layer. The larger uterine blood-vessels lie chiefly between these two layers. The cervix is composed mainly of connective tissue in which is found a large amount of elastic fibres. The cervix contains also erectile tissue of the same kind as the clitoris and the bulbs. The entire uterus, as far as it is not situated between other organs, is covered with peritoneum. The anterior surface of the uterus is almost flat and is covered with a layer of peritoneum which is inflected upon the bladder at the level of the os internum. The posterior surface is convex and covered, in its whole extent, with a layer of peritoneum which is prolonged downward for a short distance upon the posterior wall of the vagina. The anterior and posterior peritoneal coverings unite laterally and form the broad ligaments. The uterus is fixed in its place by the round ligaments. The latter are the continuations of the uterine tissue. They run between the folds of the broad ligaments and through the inguinal canals and terminate within the tissue of the labia majora. [Illustration: CUT XXI. _Schema of the internal female genital apparatus._ a, Fallopian tube; b, ovary; c, cervix; d, round ligament; e, vagina; f, uterus.] The uterus is normally anteflected, the fundus lying forward near the symphysis, and the cervix to the rear. The average length of the uterus is about seven centimeters, the breadth is about four centimeters.