Hind Limb of Fowl. 



rii 



The hind limb of the Bird differs in several important par- 

 ticulars from that of the frog. The femur, to begin with, is 

 much shorter than the tibia ; the fibula is rudimentary, and 

 does not reach far down the tibia. This bone, the tibia, is 

 followed by a long bone, with which the four toes articulate. 

 Thus the tarsus appears to be wanting. As a matter of fact, a 

 study of the immature chick shows that what is apparently the 

 tibia, is really the tibia plus the proximal elements of the 

 tarsus ; and v/hat appears to be the metatarsus is really 

 the three-fused metatarsals, plus the distal elements of the 

 tarsus. Thus the ankle-joint is not, as 

 it is in the frog and in the rabbit, be- 

 tween the end of the tibia and the 

 tarsus, but in the middle of the tarsus. 

 Hence it is more correct to apply the 

 terms " tibio-tarsus'' and " tarso-meta- 

 tarsus " to the long bones in question. 

 The metatarsal part of the tarso-meta- 

 tarsus contains, fused together, only 

 three out of the four metatarsals, those 

 corresponding to the three long toes. 

 The short hallux (or great toe) has a 

 small metatarsal, loosely attached to 

 the end of the tarso-metatarsus. The 

 bird is bipedal in its progression, as is 

 the frog to all intents. But the required 

 elongation of the limb is brought about 

 in the bird by the elongation of the 

 tibia and the metatarsus, not of the astragalus and calcaneum. 



In the Rabbit the tibia and th.e.filmla are complete, though 

 the tibia is the larger of the two. The tarsus consists of seven 

 separate bones. In the proximal row are the calcaneum and 

 astragalus ; in the middle is the cuboid ; the distal row is 

 formed by the navicular inside, and by three cuneiforms fol- 

 lowing it. There are only four digits in the foot of the rabbit. 



Mt.ni 



IV 



Fig. 53. — Hind foot of Bird. 

 (From Gadow, in Newton's 

 *' Dictionary of Birds,") 



r, tibia; F, fibula; /, tibials; 

 /, fibulare ; c, centrale ; t.d, 

 distal tarsalia ; Mt^ metatar- 

 sals. The right-hand Fig. is a 

 lateral view. 



