LIZARDS. 569 



Near the living Sphenodon, the Permian Palceohatteria, the Triassic 

 Hyperodapedon, and some other important types may be ranked. Along 

 with these may be included the remarkable Proterosaurus from the Per- 

 mian, though Seeley establishes for it a special order Proterosauria as 

 distingushed from Rhynchocephalia. According to Baur, quoted by 

 Nicholson and Lydekker, " the Rhynchocephalia, together with the 

 Proterosauria, to which they are closely allied, are certainly the most 

 generalised group of all Reptiles, and come nearest, in many respects, to 

 that order of Reptiles from which all others took their origin." We 

 have already noted how they are linked to the Amphibia. 



Class LACERTILIA Lizards. 



This class occupies a somewhat central position among 

 Reptiles. 



GENERAL CHARACTERS. The body is usually well covered 

 with scales. 



In most, both fore and hind limbs are developed and bear 

 clawed digits, but either pair or both pairs may be absent. 

 The shoulder and hip girdles are always present, in rudiment 

 at least. 



Unlike snakes, lizards have non-expansible mouths, and 

 almost always movable eyelids and external ear openings. 



The teeth are fused to the edge or to the ridge of the jaws, 

 never planted in sockets. 



The tongue, broad and short in some, e.g., Geckos and 

 Iguanas, long and terminally clubbed in Chamceleons, is 

 oftenest a narrow bifid organ of touch. 



The opening of the cloaca is transverse. 



There is a urinary bladder and a double penis. 



Most are oviparous, but in a few the eggs are hatched 

 within the body. 



They are usually active agile animals, beautifully aud often 

 protectively coloured. 



The caudal region is often very brittle ; lost tails and even 

 legs may be regenerated. 



The food generally consists of insects, worms, and other 

 small animals, but some prey upon larger animals, and 

 others are vegetarian. 



Most are terrestrial, some arboreal, a few semi-aquatic, and 

 there is one marine form. 



Lizards are most abundant in the tropics, and are absent 

 from very cold regions. 



