In a second article Schumann reviews the comparative anatomy of labor, demonstrating that the basic principles are essentially the same, alterations only being in the direction of accommodation to the pelvic construction. In order to make the analysis comparable with human conditions the pelvis is studied as if the animal were standing erect upon the hind limbs. The salient points of difference between the quadruped pelvis and the biped, human type may be epitomized as follows: (a) The entire pelvis lies (with the animal in its normal station) in a generally horizontal position with a slight slope downward anteriorly. (b) The false pelvis is almost entirely wanting, there being practically no bony structures above the brim with the exception of the small upper portions of the ilia. (c) The pelvis in quadrupeds is never basin-shaped, the lateral walls from the iliac crests to the tuberosities of the ischia lying roughly parallel to each other and enclosing a pelvic cavity rectangular in outline. Only in the highest apes does the basin-shaped pelvis appear. (d) The angle of the axis from the promontory of the sacrum to the symphysis is always greater in the quadrupeds than in man, averaging in the former from 70 to 80 degrees, in the latter about 55 degrees, (e) The symphysis pubis is an extremely long joint, being frequently greater than half the length of the entire pelvis, (f) The sacroiliac joint is more or less movable in all quadrupeds, especially in young animals. The rotation of the sacrum on the ilia increases the anteroposterior (dorsoventral) diameter of the outlet and at the same time wedges apart the ilia, thus increasing the lateral diameter. In regard to the forces of labor it is to be pointed out that in the lower mammals the pregnant uterus hangs below the pubic arch so that the fetus must rise at an angle of about 45 degrees to pass over the pelvic brim. In so doing it meets the narrowest part of the triangular bony pelvic inlet, the anterior pubic angle. Since the sacrum is above and out of the way, the lateral diameter is the one which must be suitable to the passage of the presenting part. This is the head in homo, the largest part of the fetus, but in lower animals either head or breech often accompanied by one or more extremities, may present; the head is not the largest part in lower mammalian fetuses. The uterine contraction proceeds as in man, the fundus and cornua acting alone until the cervix contains the fetus, at which time all parts contract. In the bicornate organ both sides must contract or the fetus might be forced from the gravid to the empty side. In multiparous animals with both uterine horns occupied, the fetuses lie head to head, breech to breech and are expelled alternately from each side.