THE BIRD'S PLACE IN NATURE. 5 



view and not a siihjective one; in other words, to compare and contrast tlioni 

 bodily rather than with reference to their surroundings. Morfjhology, or the 

 considerations of their structure, gives us a far better idea of their relations than 

 physiology, or the consideration i f their adaptation to their environment and 

 condition of life. The former is necessary to fully understand the latter. 



The full perception of this truth, however, was long delayed. Long after 

 its essentials had been recognized, naturalists combined the Birds with Mam- 

 mals in a group distinguished because both had warm blood and thus contrasted 

 with other vertebrates which had cold blood. Here physiological adaptation 

 was still given undue weight. The last great and vigorous upholder of this 

 view was Prof. Richard Owen, who persisted in it until his death. The insuf- 

 ficiency and irrelevancy of the character in question became at length generally 

 recognized in England, among scientitic men, in the seventh decade of the past 

 century. The appreciation of the close affinity of Birds and Reptiles was 

 largely due to Thomes H. Huxley of England and Edward D. Cope of the 

 United States. 



One of the most striking differences between Birds and other animals is 

 in the structure of the legs and the mode of combination of the tarsal bones. 

 Instead of those bones being segregated in two rows, as in mammals, the rows 

 are parted from each other, the proximal one uniting with the leg-bone and 

 forming with it a tibio-tarsus, and the distal ones equally joined to the metatar- 

 sal segments and forming a tarso-metatarsus. This structure was found to 

 be approximated in the mesozoic Dinosaurian reptiles and with this siiiiilarity 

 other structures were seen to be coincident. In fine, the relationship of the 

 Birds to Reptiles was demonstrated. Cope even went so far as to deny class 

 value to the Birds, and to consider them as only a subclass of Sauropsida, a 

 class including reptiles and birds, and several zoologists have followed him. 

 It appears to be best, however, to recognize the Birds as a class, and as a class 

 it will now be considered. 



CHARACTERS OF THE CLASS. 



The class, then, has its nearest relations in the Reptiles, but is distinguished 

 by the sum of its characters. Birds, in short, are those vertebrates which have 

 the hind limbs developed as legs, with the bones so partitioned that the proximal 

 ones of the tarsus unites with the tibia to form a tibio-tarsus and the distal ones 

 with the metatarsus to constitute a tarso-metatarsus, (the ankle joint thus being 

 interposed between the tarsal rows,) the fore limbs modified as wings, the body 

 more or less covered with feathers, the jaw bones extended into a beak and 

 covered with a specialized horny sheath in two or more pieces, the heart quad- 

 rilocular, the circulation complete, the blood warm, and reproduction ovipa- 

 rous, the egg being laid with a hard shell. 



