. A manual of zoology. Zoology. 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
. A manual of zoology. Zoology. 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 Amphis
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectzoology, bookyear1912
