530 



CHORDATA 



TejiD-E; American, teeth acroJont; Ciuiiiich^plionis,'^ Tcjiis.'^ Helodeexla.- 

 nn.t, pleuroJoiit; HcloJiniui.'' 'Gila monsters,' only poisonous lizards. 

 Laceriilid.e (Laccria) and \'ak.\md.i; (]'arjiiui, monitors) Old ^^"orld, Laccrta 

 vivipara bringing forth li\ing young. Section 1\'. Bkevilixgi'U. Tongue 

 short, slightly notched at the tip, slighdy protrusible. Scin"CID_e, with tendency 

 to reduction of the limbs. Kiimcccsr' OligosoDui.''- Aiii;iiis and TyphUnc, legs 

 absent. Zoxui^id e. Old World except Ophisjiinis vciilrdlis/" glass snake, 

 limbless, with brittle tail. Section \'. .\xxi"rAr.\. Snakedike; legs and epi- 

 pterygoid, tvmpanum, and mo\"able e\'clids lacking and usually girdles; tropical 

 or subtropical. Clnrok-.';, Ainpliishuihi. Section \'I. \'er5iilixge-ia; Old 

 World chameleons, long lleshv tongue, ring-like evelids functioning as an iris, 

 the climbing feet \\iih toes uniteil into two opposalile groups; epiptcrygoids, 

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

 changes produced by alterations of chromatophores. 



Sub Order II. PYTHOXO^IORrilA. Large, extinct, extremely elongate 

 reptiles with four flipper-like limbs and strong s\\imming tail. Flourished in 

 the cretaceous. Mosasaiinis, CliJaslts. 



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

 the absence of limbs, and connected with this the similar vertehne 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 ajipendages 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 laws. The columella is 

 indeed ])resent, 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 (oulcr conica). The jaws 

 (hgs. 572, 570) 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 bonces of the upper jaw (excep- 

 ting the small premaxillaries) and the palate. 

 Further, the squamosal (Si]), quadrate (Q), 

 and transversum (Tr) arc 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 p.iison fangs appear on the maxilla (fig. 570), distin- 

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



Fig. 5S0. — Poison fangs. .-1, 

 j4,, proteroglyphic (grooved) tootli 

 of cobra, and section of same; B, 

 Bj, solenogh'j)hic tooth (tul>ular) 

 of rattlesnake; g, poison canal; p, 

 pulp ca\ity. 



