134 SKELETON OF BIRDS. 



become confluent. The distal row consists of five bones, 

 four of \Yhicl) support the four normal toes, and the fifth, 

 a rudiment of the fifth toe without a claw: the fourth and 

 fifth of the second row of tarsals answer to the os cuboides 

 of higher animals ; the other three bones to the three ossa 

 cuneiformia. The astragal ar part of the single proximal 

 bone would seem to include the scaphoid as well as the 

 calcaneum. 



In the marine chelonia, the digits of both limbs are 

 elongated, flattened, and united bj a web ; the hands and 

 feet having the form of fins. 



In all the chelonia, the long bones of the limbs are solid, 

 without medullary cavities. 



THE SKELETON OF BIRDS. 



From the massive frame of the cold-blooded, heavy, 

 and proverbially slow tortoise, to the light, hot-blooded, 

 flying bird, the transition seems to be abrupt, and the 

 discrepancy between creatures so differently endowed ex- 

 treme ; nevertheless, at the confines of the feathered class, 

 we find some aquatic species, such as the penguin, in- 

 capable of flight, having the wings modified to act as fins, 

 and much resembling those of the turtle ; with the bones 

 solid, and the feathers resembling scales. All birds, like 

 tortoises, lay eggs, are devoid of teeth, and have their 

 jaws sheathed with horn, and forming a bill or beak. 

 Most birds, however, enjoy the faculty of flight. 



If the student of comparative osteology will procure 

 the skull of a rook, a hawk, a swan, or a sea-gull, and 

 vertically bisect it, he will have a ready instance illus- 

 trative of some of the characteristics of the osteology of 



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