252 PHYSIOLOGY AND MORPHOLOGY OF ANIMALS. 



process of the blade. In most mammals the coracoid is 

 still more reduced, and the clavicle is wanting alto- 

 gether ; but all the steps of its gradual obsolescence 

 may be picked up by extensive comparison. 



2. Elbow Joint. — In man, in monkeys, and in some 

 other mammals, and in all reptiles, the whole limb is 

 free of the body and the elbow joint halfway down the 

 limb. This is undoubtedly the original and typical con- 

 dition, but in all highly specialized mammals, by the 

 shortening of the humerus, the elbow is drawn up on 



Fig. 161. — A, fore limb of bat ; B, bird ; C, archaeopteryx ; D, pterodactyl. 

 (Lettered as in previous figure ; grouped from various sources. ) 



the side of the body so that the limb is free only from 

 the elbow downward. 



3. In man, in monkeys, and many other mammals, 

 and in all birds and reptiles, there are two bones in the 

 forearm. But in all the more specialized mammals 

 these are reduced to one, although the remnant of the 

 other is always found forming the point of the elbow 



