530 



CHORDATA 



American, teeth acrodont; Cnemidophorus* Tejus* HELODERMA- 

 TID/E, pleurodont; Heloderma,* 'Gila monsters,' only poisonous lizards. 

 LACERTILID/E (Lacerta) and VARANID.E (Varanus, monitors) Old World, Lacerta 

 vivipara bringing forth living young. Section IV. BREVILINGUIA. Tongue 

 short, slightly notched at the tip, slightly protrusible. SCINCHXE, with tendency 

 to reduction of the limbs. Eumeces* Oligosoma* Anguis and Typhline, legs 

 absent. ZOXURID.E, Old World except Ophisaurus vcntralis,* glass snake, 

 limbless, with brittle tail. Section V. AXXULATA. Snake-like; legs and epi- 

 pterygoid, tympanum, and movable eyelids lacking and usually girdles; tropical 

 or subtropical. Chirotes, Amphisbccna. Section VI. VERMILINGUIA; Old 

 World chameleons, long fleshy tongue, ring-like eyelids functioning as an iris, 

 the climbing feet with toes united into two opposable groups; epipterygoids, 

 clavicle, sternum, and tympanic membrane lacking. Celebrated for color 

 changes produced by alterations of chromatophores. 



Sub Order II. PYTHONOMORPHA. Large, extinct, extremely elongate 

 reptiles with four flipper-like limbs and strong swimming tail. Flourished in 

 the cretaceous. Mosasaurus, CUdastes. 



Sub Order III. OPHIDIA. Snakes are distinguished from most lizards by 

 the absence of h'mbs, and connected with this the similar vertebrae in which only 

 trunk and caudals can be distinguished. The caudals lack ribs, but these are 

 present and long in the trunk region, serving for locomotion and supporting the 

 body on their distal ends. Since there are legless lizards, it is further necessary 

 to say that in the Ophidia the girdles and sternum are lost, only the Peropoda 

 having remnants of the hinder appendages and pelvis, but these are not con- 

 nected with the vertebral column. The ventral side of lizards is covered with 

 scales, of reptiles with transverse scutes. 



Further distinctions exist in sense organs and jaws. The columella is 

 indeed present, but tympanum and Eustachian tube are lacking. The eyelids 



also seem to be wanting, but in front of the 

 cornea and separated from it by a lacrimal 

 sac is a transparent membrane, composed of 

 the fused eyelids (outer cornea}. The jaws 

 (figs. 572, 579) are remarkable for great ex- 

 tensibility, enabling snakes to swallow ani- 

 mals larger than themselves. This extensi- 

 bility is in part due to the fact that the bones 

 of the lower jaw are united at the symphysis 

 by elastic ligaments, in part to the freedom of 

 motion of the bones of the upper jaw (excep- 

 ting the small premaxillaries) and the palate. 

 Further, the squamosal (Sq), quadrate (Q), 

 and transversum (TV) are elongate and slen- 

 der, the quadrate being widely separated by 

 the squamosal from the skull, while the 

 zygomatic arch is entirely absent. The food 

 is forced down the throat by hook-shaped 

 teeth on palatines and pterygoids. A wide 

 distention of the stomach is rendered possible 



by^the elasticity of its walls and the great mobility of the ribs, which are not 

 united ventrally by a sternum. 



In the non-poisonous snakes the dentition is similar on jaws and palate bones 

 (fig. 572). The vomer and, usually, the premaxilla are toothless. In the 

 poisonous serpents poison fangs apoear on the maxilla (fig. 579), distin- 

 guished from the other teeth 'by their greater size and connexion with a 



B 



FIG. 580. Poison fangs. A, 

 /!,, proteroglyphic (grooved) tooth 

 of cobra, and section of same; B, 

 B l , solenoglyphic tooth (tubular) 

 of rattlesnake; g, poison canal; p, 

 pulp cavity. 



