no 



Elementary Zoology. 



unite below to form the pubic symphysis. The totally dispro- 

 portionate ilium in the bird, and possibly in the frog, also 

 seems to bear some relation to the bipedal mode of progres- 

 sion. By its extension forwards the ilium grasps more firmly 

 the welded sacral vertebrae, and thus gives a firmer support to 

 the hind limbs. 



The hind limbs of all these animals consist of a femur, 

 corresponding to the humerus of the fore limb, followed by a 



Fig. 52.— Foot of Rana temporaria. (After Howes and Ridewood.) 

 A, astragalus ; C, calcaneum : N, navicvilare (centrale) ; CU, cuboid (= fused 

 distalia 2, 3); Pli, i, 2, 3, prehallux {calcar} ;_ I, distale ; MAL, tendon 

 of adductor longus primi digiti muscle ; 1-5, digits. 



tibia and filmla, equivalent to the radius and ulna, a tarsus 

 corresponding to the carpus, a metatarsus and phalanges which 

 have also their equivalent in the fore limb. Hhe. femur of the 

 Prog is curved in a slightly S-shaped curve. The tibia and 

 fibula are here fused together to form an apparently single 

 bone. The two proximal bones of the tarsus, known respec- 

 tively as the astragalus and calcaneum, are greatly elongated. 

 This state of affairs seems to be correlated with the leaping of 

 the amphibian, for a similar modification is to be found in the 

 jumping Jerboa. The distal rows of tarsal bones are cartila- 

 ginous, and there are five complete toes, with a rudiment of a 

 sixth, in the form of a small bone known as the calcar. 



