198 EEPTILIA. 



pagos Islands ; but Dr Glinther has shown that several 

 gigantic species of Tcstudo formerly inhabited the islands 

 of Mauritius and Eodriguez. 



Order II. Ophidia. — The second order of Eeptiles is that 

 of the OjyJiidia, comprising the Snakes and Serpents, and dis- 

 tinguished by the following characters : — 



The hodi/ is cdivays more or less elongated, cylindrical, and 

 lo'orm-like, and whilst possessing a covering of horny scales, is 

 always unprovided tvith a hony exoskeleton. The dorsal ver- 

 telrce are concave in front {'proccelous), with rudimentary trans- 

 verse processes. There is never any sternum, nor pectoral arch, 

 nor fore-linibs, nor sacrutn, and, as a nde, there are no traces 

 of hind-limhs. Eudimentary hind-limbs, however, are occa- 

 sionally present (e. g., in Python and Tortrix). There are 

 cdivays numerous rihs. The two halves or rami of the lower 

 jaw are composed of several pieces, and the rami are united 

 anteriorly hy ligaments and nfiusclcs only, and not by cartilage 

 or sidure. The loioer jaw, further, articulates with the skidl 

 hy means of a quadrate hone, ivhich is alivays more or less 

 movahle, and is in turn united with the squamotis portion of 

 the temporcd hone (" 7nastoid hone "), which is also movahle, and 

 is not firmly united tvith the shull. The sup)erior maxilloe are 

 united ivith the praimaxUloi hy ligaments and muscles only, 

 and the pcdatine arches are movahle and armed with pointed 

 recurved teeth. Hooked coniccd teeth are ahvays present, httt 

 they are never lodged in distinct sockets or alveoli. Function- 

 ally, they are capable of performing nothing more than 

 merely holding the prey fast, and the Snakes are provided 

 Avith no genuine masticatory apparatus. The heart has 

 three chambers, two auricles, and a ventricle, the latter im- 

 perfectly divided into two cavities by an incomplete septum. 

 The lungs and other paired organs are mostly not bilaterally 

 symmetrical, one of each pair being either rudimentary or 

 absent. 



The vertebral column in the Snakes is always composed 

 of very numerous vertebne, which are divisible only into a 

 caudal and precaudal series. The atlas is the only pre- 

 caudal vertebra which does not bear ribs ; while in the 

 caudal region the place of ribs is taken by elongated trans- 



