Section 15. Figure 7 Shows the Pelvic Girdle and Limb of the Frog.

There is a femur (f.); tibia and fibula (t. and f.) are completely fused; the proximal bones of the tarsus, the astragalus (as.), and calcaneum (cal.) are elongated, there are five long digits, and in the calcar (c.) an indication of a sixth. With considerable modifications of form, the three leading constituents of the rabbit's pelvic girdle occur in relatively identical positions. The greatly elongated ilium (il.) articulates with the single (compare Rabbit) sacral vertebra (s.v. in Figure 5). The ischium (is.) is relatively smaller than in the rabbit, and the pubis (pu.) is a ventral wedge of unossified cartilage. The shape of the pelvic girdle of the frog is a wide departure from that found among related forms. In connection with the leaping habit, the ilia are greatly elongated, and the pubes and ischia much reduced. Generally throughout the air-frequenting vertebrata, we find the same arrangement of these three bones, usually in the form of an inverted. Y-- the ilium above, the ischium and pubis below, and the acetabulum at the junction of the three.