The =ilium= (_I_) is somewhat contracted at the middle and broader at its ends. One end enters into the acetabulum (Fig. 55, _d_) and forms about one-fifth the articular surface. This end is also the thickest part of the bone. The lateral surface of the ilium is concave for the attachment of muscles. The medial surface is smooth over its acetabular half and rough over its sacral half. The rough portion is marked at its junction with the smooth portion by the ear-shaped =auricular impression= by which the bone articulates directly with the sacrum. The caudal half of that part of the medial surface craniad of the auricular impression gives attachment to the ilio-sacral ligaments which bind the ilium to the sacrum. The dorsal border is straight at its cranial end and concave and rounded at its caudal end. Between the two portions and at the dorsal edge of the auricular surface is a protuberance corresponding to the =posterior inferior spine= (Fig. 55, _b_) of the human ilium. The concavity of the dorsal border (_c_) corresponds to the great sciatic notch of the human ilium. At its caudal end is the short =spine of the ischium= (_e_), which is not a part of the ilium. The ventral border of the ilium is broad caudad, becoming narrower craniad. The lateral margin of the ventral border is continued to a tuberosity at the edge of the acetabulum; its medial margin is called the =iliopectineal line= (_l_) and extends on the pubis to the symphysis. An eminence, the =iliopectineal eminence= (_l′_), on the iliopectineal line, lies opposite to the acetabulum at about the junction of the ilium and pubis. The cranial end of the bone is thickened, forming the =crest= (_a_) of the ilium. At the junction of the crest with the ventral border is a projection, the =anterior superior process= (_m_) of human anatomy. The =pubis= (_III_) (including the acetabular bone) enters into the formation of the acetabulum (_d_) constituting about one-sixth the circumference, but less than one-sixth its area. It may be described as a flat, curved bone, contracted at the middle and expanded at the ends. The dorsal end enters into the acetabulum; the ventral end unites with the opposite bone at the symphysis pubis and sends caudad a projection, the =ramus= (_i_) of the pubis, which unites with the ramus of the opposite bone to form about two-thirds of the entire symphysis. At the sides of the symphysis a slightly marked angle projects craniad from each of the pubic bones; these two together constitute the =pubic tubercle= (_k_), for the origin of the rectus abdominis muscle. The surfaces of the ramus are smooth. One of its borders is concave and enters into the formation of the obturator foramen (_j_). Another of its borders is the iliopectineal line (_l_). Its third border is rough for the symphysis.