The bones which form the skeleton of the pelvis of quadrupeds are proportionally more elongated and less massive than those of the human pelvis (Figs. 43 and 44). We find, on the external surface of the iliac bone, the cotyloid cavity, whose border is interrupted by the cotyloid notch; a deep notch which looks downwards. In front of this cavity is the ilium. This portion, narrow in the part which is next the cavity, is directed forwards and upwards, expanding more and more as it passes upwards. It presents an external or superior surface (external in some animals, superior in others), which recalls the external iliac fossa; and an internal or inferior surface, at the superior part of which is found the auricular surface for articulation with the sacrum. The anterior border of the ilium is rough; this is the iliac crest, at the extremities of which we find, below or outside, a prominence which corresponds to the anterior superior iliac spine of man; and internally another projection which corresponds to the posterior iliac spine. Immediately above the cotyloid cavity is a rough crest, which is known as the _supracotyloid crest_, which is, however, no other than the homologue of the sciatic spine. In front of this prominence, the border of the ilium, which is notched, forms the great sciatic notch. If, still taking the cotyloid cavity as the point of departure, we proceed inwards--that is, towards the median line of the body--we find the pubis; if in a posterior direction, the ischium. These two portions, pubis and ischium, limit an oval orifice, the subpubic foramen. In the human skeleton, the pubis of one side is united to that of the opposite side, to form the pubic symphysis. In the animals which we are now studying a portion of the ischium enters into the formation of the symphysis; in other words, it is formed, not only by the body of the pubis, but also by the descending branch or ramus of the pubis and a portion of the ascending branch or ramus of the ischium, which are fused with those of the opposite side. It results that, though in the human being the symphysis is short and the ischio-pubic arch large, in quadrupeds it is the opposite. In them the arch is a mere slot, and being formed by the ischium alone, merits the name of the ischial arch. The ischio-pubic symphysis is very large, and forms a horizontal surface relatively extensive, a sort of floor, on which rest certain organs which occupy the cavity of the pelvis.