JAWS 87 



in the same line as tlie neck, as it does in nearly all 

 fishes and amphibians; bnt in many extinct forms 

 of reptiles the head was placed at right angles to the 

 neck, as it is in the horse and so many other mam- 

 mals. This doubtless resulted from the high eleva- 

 tion of the forepart of the body in these old mon- 

 sters. All modern forms are primarily crawlers, and 

 hence the low horizontal head and neck. 



In perhaps all reptiles the size of the head is very 

 small in proportion to that of the body ; and in some 

 fossil monsters it was so absurdly small as to make us 

 feel that the creatures to which they belonged had 

 just sense enough to feed themselves and to walk 

 around. 



The heads of crocodilians have the skin tightly 

 drawn over the skull and the bones are nnich carved 

 or sculptured. The skin here is not covered with 

 horny plates or scales as it is in most lizard-forms. 

 Some lizards have beneath the skin a shield of loose 

 bones which are not a part of the skull or skeleton 

 proper. 



Jaws 



The jaws of the reptiles are very interesting to 

 the student. In all the vertebrates below the mam- 

 mals, the upper jaw has some slight movement upon 

 the skull, though it is in no sense hinged as the lower. 

 This is especially true of the beaked kinds. In the 

 crocodilians, the upper jaw appears hinged as they 

 lie flat with the mouth open, but it is really the 

 whole head that is lifted. It is true that the flat 

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