568 



REPTILIA 



[CH. 



Reptiles osteoderms extend over and cover the dermal bones of the 

 skull. 



Another characteristic of Reptiles is that the skull articulates 

 with the vertebral column by one condyle only. 



The dermal glands so characteristic of the Amphibia have 

 almost totally disappeared, being restricted to a small area, as, for 

 instance, the front of the thigh in a Lizard. It follows that a Reptile 

 is essentially a dry-skinned animal and by no means a "slimy 

 beast." 



The lungs have to some extent acquired a spongy texture, and 

 the mechanism for inhaling and exhaling air is usually to be found 

 in the ribs, not solely in the hyoid or remains of the hinder 



FIG. 279. Section through the scale of a Lizard. 



1. Epitrichial layer. 2. Heavily cornified cells forming the scale. 3. Pig- 

 ment cell. 4. Ordinary cells of horny layer. 5. Innermost Malpighian 

 layer. 6. Dermis. 



visceral arches as in the Amphibia, although these may co-operate 

 in assisting respiration. 



Living Reptiles are divided into four orders, of which one 

 consists of only one species, Sphenodon punctatus, found in New 

 Zealand. This animal is the type of the order (i) Rhyncho- 

 cephala, and is especially interesting as not only being to some 

 extent intermediate in structure between other orders of living 

 Reptiles, but as recalling very closely the structure of some of the 

 oldest fossil Reptiles known to us. The other orders are (ii) the 

 Sauria including (a) Lacertilia (Lizards), and (b) Ophidia 

 (Snakes), the (iii) Chelonia (Turtles and Tortoises) and the (iv) 

 Crocodilia (Alligators and Crocodiles). Of the four orders only 

 the second and third are represented in Great Britain and these 



