The Uterus is a hollow pear-shaped muscular organ, about three inches in length, nearly an inch thick, and about two inches broad across its upper part, or FUNDUS; the lower part, or CERVIX, being much narrower. The CERVIX, or "neck" of the womb, projects into the Vagina, forming the "os uteri," or "mouth of the womb," at that point. The Uterus is composed chiefly of a muscular coat, its walls consisting of strong muscular fibres which contract independently of the will, as do similar muscles in the stomach and bladder. These muscular walls are capable of enormous distention during pregnancy. The muscles of the healthy womb are capable of a tremendous pressure and resistance, and are capable of expelling the child with but slight labor at the time of delivery. The Uterus is located just behind and slightly above the bladder, and is supported by eight ligaments which, in a healthy condition, hold it firmly and easily in place. Displacements of the Uterus are due to the weakening or relaxing of some or all of these ligaments, generally caused by general weakness or else by excessive physical exercise or labor. The principal DISPLACEMENTS OF THE UTERUS are as follows: Prolapsus, or lowering of the womb in the vagina; Antroversion, or the bending forward of the womb; Anteflexion, or the "doubling up" of the womb FORWARD on itself; Retroversion, or the bending backward of the womb; and Retroflexion, or the "doubling up" of the womb BACKWARD on itself. Extreme degrees of the last four mentioned forms of displacement often interfere with impregnation. The internal surface of the Uterus is lined with mucous membrane thickly studded with minute hairlike cells which manifest continuous motion. This motion, in the lower part of the womb, is in the direction of the fundus or upper part of the womb; in the upper part of the womb, the motion is in the opposite direction; the purpose of these opposing movements being to carry the male elements toward that portion of the womb into which the Fallopian Tubes discharge the products of the Ovaries, as we shall see presently. The Uterus is supplied with follicles around its neck which secrete a very firm, adhesive mucus substance, which serves as a gate or door across the mouth of the womb during the period of pregnancy, and which also serves to prevent the accidental displacement of the ovum or egg. During and just after menstruation, the Uterus becomes enlarged and more vascular. During pregnancy, it largely increases in weight. After delivery, it resumes its normal size, but the cavity is larger than before conception. In old age, it becomes atrophied and denser in structure.