5 6S 



REPTILES. 



also a single tooth on each side of a kind of beak formed by the pre- 

 maxillse ; the nares are divided. 



The vertebrae are amphiccelous or 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 numerous " abdominal 

 ribs," ossifications in the subcutaneous fibrous tissue of the abdomen. 

 The anterior end of the "plastron" thus foimed overlaps the posterior 

 end of the sternum. Clavicles and interclavicle or ■ episternum are 

 present. 



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 Sphenodon, the Permian Palaohatteria, the Triassic 

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

 with[these may be included the remarkable Proterosaurus fiom the Per- 

 mian, though Seeley 

 establishes for it a 

 special order — Pro- 

 terosauria, as dis- 

 tinguished from 

 Rhynchocephalia. 

 According to Baur, 

 quoted by Nicholson 

 and Lydekker, ' ' the 

 Rhynchocephalia, to- 

 gether with the Pro- 

 terosauria, to which 

 they are closely allied, are certainly the most generalised group of all 

 Reptiles, and come nearest, in many respects, to thatorder of Reptiles 

 from which all others took their origin. " We have already noted that 

 they are linked to the Amphibia. 



Fig. 247. — Hatteria or Sphenodon. — After 

 Hayek. 



Lacertilia. Lizards. 



The lizards occupy 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. There is a sternum and an episternum. 

 Unlike snakes, lizards have non-expansible mouths. The 

 maxilla, palatines, and pterygoids are fixed, and there is 

 usually a mandibular symphysis. There are 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 



