LIZARDS. 406 



Oeder III. — LACERTILTA. 



To this order beldiii;- llie li/.arils, u liich may 1h' (Ii-HiumI as all now existing reptiles 

 having a pectoral girdle and stermnn, and, as a rule, four linihs. A tyni]ianic cavity 

 is usually present, and the eyes, witli a few e.xcejjtions only, arc provided with lids. 

 The bones of the jaws and luad di not allow that expansibility generally character- 

 istic of snakes, and a still further dejiarture is made from this group in that the lizards 

 are provided with a urinary bladder. 



The lizards are generally of an elongated form, and snake-like, some carrying the 

 resemblance still further by liaving the limbs reduced to rudiments, or externally en- 

 tirely absent. The limbs, when present, are seldom sufficiently strong to support the 

 body from the grouml, and are hence used more as pushing organs, though the cha- 

 meleons have them designed for grasping, the geckos Tnodified into sucking disks, l)y 

 which they can ascend perjiendlcular walls, some of the iguanas for swimming, and 

 yet others for digging. It will thus be seen that the animals are designed for differ- 

 ent modes of life. While some lizards are terrestrial, and have the limbs poorly 

 developed or even absent, others are arboreal, and, like the arlioreal serpents, are spe- 

 cially modified and jirotectively colored. It is in this order, however, that we first 

 find rejitiles designed for an aC'rial, or jiartially aerial, life. The shoulder girdle is 

 always present, and the shape of the clavicle is of considerable taxonomic value. The 

 sternum is absent in a single genus, Amphi$b(ena. The ribs are generally present, 

 and extend from the anterior cervical to the lumbar vertebra;. These ribs, in forms 

 like Draco and Liole})his, are the chief organs of support for the wing-like expansions 

 of the sides of the body. 



The structure of the skull is particularly interesting, though complex. On its 

 peculiarities has been based the only natural classification. The cranium proper, that 

 portion of the skull enclosing the bi'ain, is relatively small ; it does not extend to the 

 orbital region, and is protected in front by a vertical curtain, the membranous inter- 

 orbital sejitutn. The bones of the jaw are connected with those of the cranium by 

 the intervention of an arch, the zygomatic, made up of the malar, postorbital, and 

 squamosal bones. The quadrate is large and much more firmly attached than in either 

 of the previous orders. The rigidity with which the bones are united is worthy of 

 notice, and ]iartieularly interesting when compared with the loosely articul.ated facial 

 bones of the ser2:)ents. The lower jaw is incapable of lateral expansion, cither by 

 means of an elastic symphysis, or by a medial joint. 



The dentition is ))eculiar, and, to a certain extent, characteristic. Much more 

 variety as regards general structure, mode of- insertion, and position of teeth, is pre- 

 sented than in the previous orders, though these peculiarities are of only secondary 

 value in classification. In many families there is an interesting distinction lietween 

 Old and New World forms ; the former having the teeth planted along the ridge of 

 the jaw are termed arrodonf, while the latter have them merely appresscd to the 

 inside, and are p!in-odont. A jieeuliar anomaly is presented by the American genus, 

 Teiiis, the teeth in the young being jilurodont, and, as age j)roceeds, by a growth of 

 the bone of the jaw around their bases gradually becoming acrodont. 



Though the shajie of the tongue is very variable, and, to a certain extent, charac- 

 teristic, its covering is of far more importance to the systematic zoologist. Though 

 the lower families an<l the degraded Amiihisba'nas have the eyes, like the serpents, 



