CHARACTERS OF REPTILES 
CHAPTER VIII 
Reptiles 
HE reptiles are the only vertebrates which are 
cold-blooded and which without exception 
breathe by lungs and never at any period of their 
lives breathe by gills, as do the fishes always and the 
amphibia for a portion of their lives. They have also 
invariably a scale-covered skin, in which also there may 
be supplementary bony structures, such as the bony 
part of the “box” of the tortoise, and the strong 
plates in the skin of crocodiles. They possess neither 
feathers nor hairs. The skull is fixed on to the suc- 
ceeding vertebral column by one rounded joint or con- 
dyle as in birds, while the mammals and the amphibia 
have two of these, one on each side. It is from the 
amphibia that it is most difficult to divide reptiles, a 
fact which is embodied in the confusion of the two into 
one group, called “reptiles”? by some of the older 
authors, and “amphibia’”’ by some others. In past 
times, as is natural on any theory of evolution, the 
reptilia and the amphibia gradated into one another, 
and no very hard and fast line can be drawn. The 
living representatives of these groups can, however, 
be distinguished by the characters already enumerated. 
There are other anatomical characters into the con- 
sideration of which we shall not enter here. The most 
obvious character of the reptile is its complete covering 
of scales. Some extinct groups, such as the Ichthyo- 
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