CHAPTER XVI. 



GENERAL ACCOUNT OF THE SKELETON IN 

 REPTILES. 



EXOSKELETON. 



The exoskeleton both epidermal and dermal is exceedingly 

 well developed in reptiles. 



EPIDERMAL EXOSKELETON. 



This generally has the form of overlapping horny scales 

 which invest outgrowths of the dermis, and are found covering 

 the whole body in most Rhynchocephalia, Ophidia, and Lacer- 

 tilia, and many Crocodilia. In the Ophidia the ventral surface 

 of the tail is commonly covered by a double row of broad scales, 

 while the ventral surface of the precaudal part of the body is 

 covered by a single row. In the burrowing snakes (Typhlo- 

 pidae) and some sea snakes (Hydrophidae) these broad scales 

 do not occur, the scales of the ventral surface being similar to 

 those of the dorsal. 



In the Chelonia with the exception of Dermochelys, Trionyx 

 and their allies there is a well-developed system of horny shields 

 having a regular arrangement which has been described in the 

 account of the Turtle's skeleton 1 . 



The rattle of the rattlesnake is an epidermal structure 

 formed of several loosely articulated horny rings, produced by 

 the modification of the epidermal covering of the end of the 

 tail, which instead of being cast off when the rest of the outer 

 skin is shed is retained loosely interlocked with the adjoining 



1 See pp. 214 and 215. 



