Internally the urethra opens into the bladder. Its direction is subject to variation during pregnancy, the bladder being carried upwards with the uterus, the urethra curves under the pubic arch, and then ascends perpendicularly. The same change occurs when the uterus is enlarged from other causes. In prolapse of the pelvic viscera the course is reversed. The PERINEUM is the portion between the rectum and the vagina. THE UTERUS. The uterus is the organ provided for the reception, growth, and ultimately for the expulsion of the fœtus. In the virgin normal state it is pear-shaped, flattened from before backwards; is situated in the cavity of the pelvis, between the bladder and the rectum, and projects into the upper end of the vagina below. Its upper end or base is directed upwards and forwards, so that its axis corresponds very nearly with that of the superior strait, and forms an angle with the vagina. The uterus measures about three inches in length, at its upper part two in breadth, an inch in thickness, and it weighs from one ounce to an ounce and a half. The _fundus_ is the upper broad extremity of the organ; it is convex, covered by peritoneum, and placed in a line below the level of the brim of the pelvis. The _body_ gradually narrows from the fundus to the neck. Its anterior surface is flattened, covered by peritoneum in the upper three-fourths of its extent, and separated from the bladder by some convolutions of the small intestines; the lower fourth is connected with the bladder. Its posterior surface is convex, covered by peritoneum throughout, and separated from the rectum by some convolutions of the intestines. The lateral margins are concave, and give attachment to the Fallopian tubes above or superiorly, and the round ligaments below; and behind these, and also below the ligament of the ovary. The _cervix_ is the lower and constricted portion of the uterus; around its circumference is attached the upper end of the vagina, and this extends upwards a greater distance behind than in front. At the vaginal extremity of the uterus is a transverse aperture, the OS UTERI, bounded by two lips, an anterior one which is thick, and a posterior one, narrow and long. The os uteri, or os tincæ, is generally about the size of a small goose-quill. The _canal of the cervix_ is from half to three-quarters of an inch long; leading from the os uteri it first widens and then contracts again where it enters the body of the uterus. The surface of the canal exhibits a variable number of follicles or vesicles called the _glandula nabothi_, which secrete a thick mucus; this blocks the canal after impregnation. The cavity of the body and neck has a longitudinal extent of about two and a half inches; in virgins it is much less. (Fig. 12). [Illustration: Fig. 11 Uterus, bladder, etc., showing relative position.