Inversion of the uterus is one of the common accidents of labor among all animals, most frequently seen in ruminants. It is a condition more to be expected in lower animals than in man because of the long slender relaxed suspensory ligaments, the length of the uterus and the rigor of the contractions. The immediate causes are those operative for human beings. Three cases are recorded—one in an axis deer, one in an opossum, one in a mouse, the last being detailed in the following notes: A Japanese Waltzing Mouse (_Mus wagnerii rotans_) died a few hours after an uneventful labor. On autopsy the entire uterus was found inverted and prolapsed, the organ the seat of a violent congestion, the animal having died of shock. [Illustration: FIG. 22.—INVERTED AND PROLAPSED UTERUS. JAPANESE WALTZING MOUSE (MUS WAGNERII ROTANS). UTERUS SHOWN LYING ON CARD. ] THE PELVIS. A study of the dynamics of the female pelvis from an evolutionary standpoint may explain some of the difficulties attending parturition. Starting from the biological law that morphology follows function and that the anatomy of a part alters to suit a changed physiology with such modifications as are necessary to fit each part properly to interact with other structures comprising the entire animal, it is evident that two great changes have occurred in the evolution of homo—the assumption of the upright posture and an increase of intellectual power necessitating a larger cranium of modified form. To this end also the pelvis would have to change both for support and to allow the passage of the enlarged head. The functions of the pelvis are (1) to attach the legs or hinder limbs to the trunk; (2) to furnish points of attachment and fulcra for the great muscles which move the limbs, and in the case of man, hold the trunk erect; (3) to provide egress and support for the terminal canals of the intestinal and urinary systems; (4) to provide for a birth passage; (5) to act as a shelf and support for the abdominal viscera. In quadrupeds the first four functions being perfectly served, there are fewer abnormalities of reproduction (and in the positions of viscera as well—ED.). In man natural selection weeded out narrow pelves, but the present product is as yet an imperfect structure for one of its main uses, parturition. It should be a funnel-shaped basin of the shape of the fetal head and of the same height at all points—that is not oblique, there should be no promontory, the pelvic symphysis should be short and the sacrum of the same height. This would obviate internal rotation now necessitated by the oblique pelvis; this does not occur in quadrupeds.