LIZARDS. 475 



away ; there is also a single tooth on each side of a sort of 

 beak formed by the premaxillae ; the nares are divided. 



The vertebrae are biconcave, as in geckos among lizards 

 and in many extinct Reptiles. Some of the ribs bear 

 uncinate processes, as in Birds ; as in crocodiles, there are 

 " abdominal ribs," ossifications in the sub-cutaneous fibrous 

 tissue of the abdomen. 



The pineal or parietal eye, which reaches the skin on the 

 top of the head, is less degenerate than in other animals, 

 retaining, for instance, distinct traces of a complex retina. 



Near the living Haiteria, the Permian Palaohatteria, the 

 Triassic Hyperodapedon, and some other important types 

 may be ranked. Along with these may be included the 

 remarkable Proterosaurus from the Permian, though Seeley 

 establishes for it a special order Proterosauria as distinguished 

 from Rhynchocephalia. On page 6, I have used the term 

 Proterosauria as if it were equivalent to 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 gene- 

 ralised group of all Reptiles, and come nearest, in many 

 respects, to that order of Reptiles from which all others took 

 their origin." 



Order LACERXiLiA^Lizards. 



This order occupies a somewhat central position among 

 Reptiles. 



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 Chamseleons, is 

 oftenest a narrow bifid organ of touch. 



The opening of the cloaca is transverse. 



