ii SKELETONS OF BIRD AND REPTILE 17 



not, as in mammals and most reptiles, entirely of 

 bone, and it has vanished. But ankylosis or fusion is 

 perhaps the most marked characteristic of a bird's 

 Leg. There are the same bones as in the lizard's leg, 

 if we could only see them — viz. : Femur (FE, fig. 2) 

 or thigh-bone, Tibia (T), Fibula (F), two rows of 

 Tarsals or ankle-bones (TA), four of the lizard's five 

 Metatarsals (MT), though of one of the four only the 

 farther end (MT P fig. 2) remains, and four of his five 



Fig. 6.— Hatteria Lizard's left hind foot. 

 4, 5, digits ; f, fibula; MT, metatarsals ; t, tibia; taj, two bones fixed, 

 represents near row of tarsals ; ta-_>, distant row. 



digits. The Femur has not undergone so much 

 change, but the Tibia and Fibula (fig. 3) are very 

 different from the corresponding bones in reptiles. 

 The latter has nearly vanished ; it is a slender, almost 

 needle-like bone, attached to the side of the Tibia and 

 not reaching to its farther end. In many mammals 

 too the Fibula is but a remnant. The way to make 

 certain, in the skeleton of any animal whatever, which 

 bone is the Tibia and which the Fibula, is to imagine 

 the limb extended, as it is in the lizard, outwards from 

 the body ; then the Tibia is praeaxial and the Fibula 



C 



