IV. VERTEBRATA: REPTILIA. 



589 



of distinction must be emphasized. The most important are two : 

 the reptiles belong to the Amniota and, as such, have the em- 

 bryonal features of the group; second, although often aquatic, 

 they are, in the entire absence of branchial respiration, in character 

 of skin and skeleton, in their entire structure, like the true land 

 animals. 



The skin, the better to withstand desiccation by the air, is 

 strongly cornified, so that in the epidermis a many-layered stratum 

 corneum and a many-layered stratum Malpighii can be distin- 

 guished. At the tips of the toes the stratum corneum develops 

 strong claws. Further protection is afforded by the thick derma, 

 often capable of being tanned into leather, in which not infre- 

 quently bony plates occur. Dermal glands are very rare, the 

 femoral pores of the lizards (fig. 625, &), which appear like the 

 ducts of glands, being produced by the ends of cornified epithelial 

 cones. The axial skeleton, both skull 

 and vertebral column, is nearly always 

 ossified; only exceptionally (Splieno- 

 don and the amphiccele Ascalabotae) 

 are considerable parts of the noto- 

 chord retained. The vertebrae 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 mam- 

 mals. 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 it and the 

 cranium. Behind it is the columella, 

 its inner end inserted in the fenestra 

 ovalis. From the quadrate the palatine 

 series of bones pterygoid, palatine, 

 vomer extends forward, these being 

 frequently toothed; and in front of and parallel to it the pre- 



FIG. 619. Ventral view of skull of 

 Tropidonotus. (From Wieders- 

 heim.) Bp.basioccipital; B*, basi- 

 sphenoid (in front also parasphe- 

 noid); C7i, choana; Cocc, occipital 

 condyles; Eth, ethmoid cartilage; 

 F, frontal; Fo, fenestra ovalis; 

 M, maxillary ; of, exoccipital; 7, 

 parietal; P/, pref rental; P7, pal- 

 atine ; Pmx, premaxillary ; Pf, 

 pterygoid r Qu, quadrate; Squ, 

 squamosal; Ts, transversum ; Vb, 

 vomer ; II, optic foramen. 



