n8 REPTILES 



theless, all these spiny developments appear to be for the same 

 purpose — namely, defence — as the bony spines of the dinosaurs, 

 and therefore afford an example of how the same object is 

 attained by different ends. Some of the leading types of bony 

 armature in different orders of reptiles may now be passed in 

 review, commencing with that of lizards. 



The members of several families of lizards have bony plates 

 in the skin beneath the scales, among these being the small 

 Mexican group of Xenosauindce, the girdle-tailed lizards {Zonur- 

 idce), the blind-worms and their allies {Anguidcs), the poison- 

 ous lizards (Helodermatidtz), the African Gerrhosauridce, and 

 the skinks (Scincidcz). No more beautiful example of this 

 armour exists than that of the glass-snake, or scheltopusik 

 (Ophisaurus apus), a member of the Anguidce, in which it forms 

 a solid, although flexible, mosaic-like sheath investing the long 

 snake-like body, and constituting, when cleaned, an exquisite 

 structure. In the possession of this panoply the scheltopusik 

 presents a contrast to the true snakes, in all of which it is 

 lacking. In the girdle-tailed lizards the members of the typical 

 Zonarus are covered with a coating of imbricating horny scales 

 terminating in sharp spines which are largest on the neck, 

 occiput, and tail in Z. giganteus. These are underlain by bony 

 plates forming the basis of the spines, so that the armour is 

 comparable to that of the dinosaurs. 



In the New Zealand tuatera (Sphenodon punctatus), the living 

 representative of the order Rhynchocephalia, the middle line of 

 the hind portion of the head, back, and tail is surmounted with 

 a row of partially erectile spines apparently similar to those of 

 the iguanas. The tuatera's spines are said, however, to be of 

 dermal origin and are covered with a thin sheath of horn, so 

 that they seem structurally similar to those of the mail-clad 

 dinosaurs. 



All existing crocodiles and the great majority of their 

 extinct relatives possess an effective dermal armour, consisting 

 of movably articulated plates of bone overlain by horny 

 shields. Most of these plates, as well as the upper surface of 

 the bones of the skull have a pitted, or almost honey-combed 

 structure, as is frequently the case when the greater part of the 

 true skin is ossified. In modern crocodiles the plates of the 

 dorsal buckler are arranged in more than two longitudinal 



