54 THE STORY OF REPTILE LIFE. 



Eeptiles, is completely invested in a covering of 

 horny scales ; and underlying these, in certain 

 parts of the body, is an armour-plating of bone. 

 The more important features of these scales, and 

 of the bony armour, we propose now to briefly 

 outline. 



If these scales be carefully examined, there 

 will be found in the centre of each of those of 

 the sides, belly, and tail, and especially those of 

 the lower jaw, a little dot or pit. At this spot 

 the scale is soft, and at the bottom of the pit, 

 careful dissection would show the delicately 

 sensitive terminations of a nerve. On the lower 

 jaw instead of a pit we find little wart-like 

 prominences, also provided with sensory nerves. 

 Through these delicately constructed channels 

 the body is kept in touch with the outer world. 



The bony armour is made up of a series of 

 closely interlocked square plates, each plate 

 corresponding in size to the horny scale above 

 it, and having a peculiar honey-combed appear- 

 ance on the outer surface. In the majority of 

 living Crocodiles this armour is confined to the 

 upper surface. A large cluster occurs in the 

 neck, and behind this follows a huge shield in- 

 vesting the whole of the back. Only in the 

 Caimans (p. 69) do we find similar bony plates 

 on the belly. 



Why this armour was originally assumed, and 

 why it is still retained, we can only guess. 

 Probably it was developed as a protection against 

 collision with rock and tree-trunks in time of 

 flood. There seems some foundation for this view 

 inasmuch as the fossil species .Metriorhynchus 



