62O 



REPTIL1A. 



A.C 



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 formed overlaps the posterior 



end of the sternum. The inner ends of the clavicle rest on a median 



episternum (interclavicle). 



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 Palaohatttria, 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 Rhyncho- 

 cephalia. According to Baur, 

 quoted by Nicholson and 

 Lydekker, "the Rhyncho- 

 cephalia, 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." 



PC 



Order LACERTILIA 

 Lizards 



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 pectoral and 

 pelvic girdles are always present, in rudiment at least. 

 There is a sternum and a T-shaped 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 



FlG. 338. Hyoid apparatus of a 

 Chelonian. 



BH., Body of the hyoid (basihyal); 

 H., representing another part of the 

 hyoid arch; A.C., anterior cornu, 

 representing the first branchial 

 arch ; P.C., posterior cornu, repre- 

 senting the second branchial arch. 



