CLASSIFICA TION OF VER TEBRA TES. 

 Pa -^-^=^r===^ JPr 



. w 



Ha 



O/iO 



FIG. 312. Side and sectional veins of skull of Cyclodtis, from Huxley. Ar, 

 articulare; BS, basisphenoid ; BO, basioccipital ; Co, columella; D, dentary; 

 EO, exoccipital ; Fr, frontal ; EpO, epiotic ; Ju, jugal ; MX, maxillary ; Na, nasal ; 

 Pa, parietal; Pf, postfrontal ;Pmx, premaxillary ; PI, palatine; Pt, pterygoid ; PrO, 

 prootic; OpO, opisthotic; Prf, prefrontal ; Qu, quadrate; SO, supraoccipital ; Sq, 

 squamosal ; Tr, transversum ; Vo, vomer ; V, VII, passages for fifth and seventh 

 nerves. 



SUB-ORDER i. LACERTILIA (SAURII). 



Scaled or plated reptiles usually with two pairs of feet ; vertebrae 

 rarely amphicoelous; premaxilla single or paired. Postorbital arcade some- 

 times entire, jugal arch never complete. Ali- and orbitosphenoids not 

 ossified ; shoulder girdle always present. Sternum and episternum usually 

 present. Feet sometimes rudimentary or absent ; when present, usually 

 five-toed and ambulatory ; the maxilla, palatines, and pterygoids cannot 

 move on the bones of the skull, and the mouth can be opened to but a 

 moderate extent. Movable eyelids, tympanic cavity and membrane usu- 

 ally occur. The arteries supplying the alimentary canal are extremely 

 variable. 



The lizards in their outward appearance resemble closely the crocodiles 

 and Sphenodon, but in structure they have many and important points of 

 difference. The apodal forms are strikingly snake-like ; but these may be 

 distinguished in most cases at a glance by the presence of eyelids and 

 small scales instead of broad abdominal scutes on the ventral surface of 

 the body. The lizards are largely insectivorous, and only one has the repu- 



