IV. VERTEBRATA: REPTILIA. 



521 



Class I. Reptilia. 



On account of similarity of form, the reptiles and Amphibia were long 

 untied. They form parallel groups: urodeles and lizards, frogs and 

 turtles, caxilians and snakes. Hence the points of distinction must be 

 emphasized. The most important are two: the reptiles belong to the 

 Amniota and, as such, have the embryonal features of the group; second, 

 although often aquatic, they are, in the entire absence of branchial respira- 

 tion, in character of skin and skeleton, in 

 their entire structure, like the true land 

 animals. 



The skin, the better to withstand desic- 

 cation by the air, is strongly cornified, so 

 that in the epidermis a many-layered 

 stratum corneum and a many-layered 

 stratum Malpighii can be distinguished. 

 At the tips of the toes the stratum corneum 

 develops strong claws on the dorsal side, 

 the claw plate being better developed than 

 the ventral claw sole. Further protection 

 is afforded by the thick corium in which 

 not infrequently bony plates occur. 

 Dermal glands are very rare, the femoral 

 pores of lizards (fig. 577, b), which appear 

 like the ducts of glands, being produced 

 by the ends of cornified epithelial cones. 

 Here must be mentioned the dorsal, anal 

 and musk glands of the crocodiles. 



The axial skeleton, both skull and 

 vertebral column, is nearly always ossified; 

 only exceptionally (Sphenodon and the am- 

 phiccele Ascalabota?) are considerable parts 

 of the notochord retained. The vertebra? 

 are usually proccelous. In the skull of 

 reptiles (as in the allied birds) are many 

 characters which they share with Amphibia and which distinguish them 

 from mammals. This is especially the case with the visceral skeleton. 

 As in the Amphibia, the hinder end of the pterygoquadrate is attached 

 to the otic capsule; the quadrate is ossified and affords the articulation 

 for the lower jaw, which is composed of many bones. The squamosal lies 

 at the base of the quadrate and, in the Squamata, is intercalated between 



FIG. 572. Ventral view of 

 skull of Tropidonotus (from 

 Wiedersheim). Bp, basioccipital; 

 Bs, basisphenoid (in front also 

 parasphenoid); Ch, choana; Cocc, 

 occipital condyles; Iilh, ethmoid 

 cartilage; F, frontal; Fo, fenestra 

 ovalis; M, maxillary; ol, exoc- 

 cipital; P, parietal; Pf, pref rental; 

 PI, palatine; Pmx, premaxillary; 

 Pt, pterygoid; Qu, quadrate; Sgit, 

 squamosal; Ts, transversum; Vo, 

 vomer; //, optic foramen. 



