176 ANIMAL BIOLOGY. [Part I. 



tarsal articulation. The hallux has two phalanges ; the second, 

 third, and fourth digits have three, four, and five phalanges 

 respectively. Both the hind and fore-limb of the bird are thus 

 seen to be remarkably modified. 



In the frog the femur is a thin elongated bone. The tibia 

 and fibula fuse together into a tibio-fibula, which shows signs, 

 even in the adult, of its compound origin. The astragalus and 

 calcaneum are remarkably elongated, fusing to a considerable 

 extent at their ends. They aid in giving the extreme length 

 to the pes. The distal row of the tarsals is represented by two 

 partly ossified cartilages. There are five metatarsals and five 

 well-developed digits, and, in addition to these, the cakar, which 

 is situated on the radial side ; it is composed of two or three 

 pieces, and may represent a sixth digit. 



For the changes of position which the hind-limbs have under- 

 gone see Chapter II., pp. 7, 14, and 19. 



