AMPHIBIA. 187 



of the two " prongs " or ilia fused in the middle line. Each 

 ilium is continued forwards to the sacrum, to the corresponding 

 transverse process of which its cartilage-tipped end is united. 

 This part of the ilium is laterally flattened, with somewhat 

 concave ventral and convex dorsal edges. Two other elements 

 on either side, pubis and ischium, of which the first is cartilaginous, 

 unite with their fellows to form the middle and posterior parts 

 of the plate and acetabulum. The pubes are triangular, and their 

 apices extend to the upper margin of the acetabulum, above which 

 the ilia and ischia unite. 



The free limb is composed of bones belonging to the thigh, leg, 

 and foot. The first is supported by a long bone, the femur, the 

 slender shaft of which possesses a slight double or sigmoid curve. 

 Its proximal end is enlarged into a rounded head, which articulates 

 with the acetabulum to form the hip- joint, and its distal end also 

 presents an articular expansion. The bone of the leg, tibio-fibula, 

 like that of the fore-arm, is compound. It is made up by the 

 fusion of a pre-axial tibia with a post-axial fibula, the boundaries 

 of which are indicated by grooves and a double marrow-cavity. 

 The shaft is curved, and the ends are expanded into transversely 

 elongated pulleys, which assist in the formation of the knee- and 

 ankle-joints respectively. The bones of the foot are partly those 

 of the ankle, tarsus, and partly those of the digits. The typical 

 or theoretical tarsus contains the same number of elements as the 

 theoretical carpus, and these are similarly arranged, as follows : 

 [T = tibial or pre-axial side ; F = fibular or post-axial side.] 



T F 



tibiale intermedium fibulare 



centrale 



tarsale 1 tarsale 2 tarsale 3 tarsale 4 tarsale 5 



The tarsus of the frog is very much elongated, and composed 

 of four bones, two of which are proximal and two distal. The 

 proximal ones, astragalus and calcaneum ( = tibiale + intermedium, 

 and fibulare), articulate with the tibial and fibular sides of the 

 articular surface on the distal end of the tibio-fibula. They are 

 united to each other at either end by their epiphyses. The distal 

 bones, equivalent to the tarsalia, are extremely small. One, 



