The =ischium= is large. Its long axis is directed obliquely upward and backward, forming an angle of about 45 to 50 degrees with the horizontal plane. The transverse axis is oblique downward and inward at a similar angle, so that this part of the pelvic floor is deeply concave from side to side. The middle of the ventral surface bears a rough ridge or imprint for muscular attachment. The superior ischiatic spine is high and thin, and bears a series of almost vertical rough lines externally. The tuber ischii is large and three-sided, bearing upper, lower, and external tuberosities. The ischial arch is narrow and deep. The symphysis bears a ventral ridge, which fades out near the ischial arch. The acetabular branch of the =pubis= is narrow, and is directed outward and a little forward. The anterior border is marked by a transverse groove which ends below the rough ilio-pectineal eminence. The longitudinal branch is wide and thin. The =acetabulum= is smaller than in the horse. The rim is rounded and is usually marked by two notches. One of these is postero-internal and is narrow and deep; it leads to the deep acetabular fossa and is commonly almost converted into a foramen by a bar of bone. The other notch is antero-internal, small, and sometimes replaced by a foramen or absent. The =obturator foramen= is large and elliptical. Its inner border is thin and sharp. [Illustration: FIG. 101.—SKELETON OF LEFT HIND LIMB OF OX, FROM MIDDLE OF THIGH DOWNWARD, POSTERIOR VIEW. _21_, Tibia; _24_, tuber calcis; _25_, large metatarsal bone. (After Ellenberger-Baum, Anat. für Künstler.) ] The =pelvic inlet= is elliptical and is more oblique than in the horse. In a cow of medium size the =conjugate diameter= is about nine and a half inches (ca. 23 to 24 cm.), and the transverse about seven inches (ca. 18 cm.). The anterior end of the symphysis lies in a transverse plane through the junction of the third and fourth sacral segments. The roof is concave in both directions. The =floor= is deeply concave, particularly in the transverse direction. The =cavity= is narrower and its =axis= is inclined strongly upward in the posterior part. The distance between the acetabulum and the external angle of the ilium is only a little (ca. 3 to 4 cm.) more than the distance between the former and the tuber ischii. [Illustration: FIG. 102.—FRONTAL SECTION OF LEFT FEMUR OF OX, FRONT VIEW. ] [Illustration: FIG. 103.—FRONTAL SECTION OF LEFT TIBIA OF OX, ANTERIOR VIEW. These figures show the internal architecture of these bones, and especially the great extent of the medullary cavity as compared with those of the horse (Figs. 67 and 72). ]