PROFESSOR HUXLEY'S LECTURES. 



221 



back-bone, between the two haunch -bones, are united so as to 

 form a solid support upon which the weight of the body rests. Then 

 the thigh-bone becomes very short, and has a back ridge upon its outer 

 articular surface. At the lower end the ridge tits in between the 

 upper extremity of the small bone of the leg, near to the great bone, 



Fig. (J. Bird. 



Dinosaur. 



Crocodile. 



and makes a kind of spring-joint. The small bone of the leg is quite 

 large above, and becomes rudimentary below. It runs out into a 

 style, instead of being long and large, as it is in the case of the croco- 

 dile. Then, when you come to the bones of the foot, you find there 

 are no separate bones such as you have here, but the end of the tibia, 

 or large bone of the leg, appears to end in a kind of pulley, a sin- 

 gle bone follows the tibia and to the trifurcated extremity of this 

 bone. Upon the extremity of that bone are attached three toes. It 

 is obvious that the contrast between the crocodile's leg on the one 

 hand, and the bird's leg on the other, is very striking. But this in- 

 terval is completely filled up when you study the character of the 

 hinder extremities in those ancient reptiles which are called the Dino- 

 scmria. In some of these the bones of the pelvis, and those of the 

 hind-limb, become extraordinarily similar to those of birds, especially 

 to those of young or foetal birds. Furthermore, in some of these rep- 

 tiles, the fore-limbs become smaller and smaller, and thus the sus- 

 picion naturally arises that they may have assumed the erect posi- 

 tion. That view was entertained by Mantel, and was also demon- 

 strated to be probable by your own distinguished anatomist, Leidy, 

 but the discoveries of late years -show that in some of these forms the 



