IV. VERTEBRATA: REPTILIA, SQUAMATA 



529 



inconspicuous true cuticle. Since all cornified cells are dead and require 

 periodic removal, the horny layers are cast yearly and replaced by new. 

 During this periodic molting, which recalls that of arthropods, the animals 

 are sickly and apt to die in captivity. 



All Squamata are characterized by the slenderness of the cranial bones 

 (figs. 572, 578, 579), which, especially in the Lacertilia, incompletely 

 close in the cranium. The quadrate is movable, and the squamosal is 

 intercalated between it and the cranium. A hard palate is lacking, and 

 the choanae, as in the amphibia, lie far forward (fig. 572, Ch). There is 

 a wide gap in the partition between the two ventricles of the heart. 



Sub Order I. LACERTILIA (Saurii). The lizards are usually distin- 

 guished from the snakes by the possession of limbs, but a few undoubted lizards 

 (glass snakes and Amphisbsena;,) lack limbs. These are distinguished by the 

 existence of the scapula and the iliac bone united to the vertebra, and the 

 presence of a sternum, which never occurs in snakes. In the skull is a peculiar 

 bone (lacking only in Chameleons and Amphisbaenas), found nowhere else, the 

 epipierygoid (fig. 578, co); it reaches from the pterygoid to the parietal, and is 

 sometimes called columella (not to be confounded with the true columella of the 



ITFrf Fr 



Fig. 579. — Skull of rattlesnake (from Boas). Fr. frontal; h, hyomandibular 

 (columella); Mx, maxillary; N , nasal; Os, supraoccipital; Pa, parietal; Pal, palatine; 

 Pf, postfrontal; Prf, prefrontal; Pi, pterygoid; Px, premaxilla; Q, quadrate;5g, squamo- 

 sal; Tr, transversum; i, dentary; 3, articulare. 



ear). The bones of the jaws are firmly united, so that the mouth has no special 

 capacity for opening widely. The jugal-quadratojugal arch is present. In 

 external appearance the presence of eyelids, nictitating membrane, tympanic 

 membrane, and Eustachian tube are noticeable, these being absent only in the 

 Amphisbeenas. In the Ascalabota:, as in snakes, the lids grow together, forming 

 a transparent covering over the eyes. The grcSup dates back to the cretaceous. 



Section I. Ascalabot^ (geckos). Skeleton incompletely ossified, notochord 

 persistent, amphicoele vertebrae ; skin granular, usually adhesive discs on toes, Pliyl- 

 lodactylus* Section II. Crassilinguia. Tongue thick, fleshy, not protrusible. 

 IguaniD/E; American, often a comb of spines on back, teeth pleurodont, i.e., 

 united to inner side of jaw. Anolis,'-^ Sceleponts* Phrynosoma,* 'horned toads.' 

 Agamid.5:; Old World, teeth acrodont, i.e., on the edge of iaw. Chlamydosaurus, 

 Draco. Section III. Fissilinguia. Tongue long, thin, divided at tip, protrusible. 

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