372 CROCODILIA. 



Sistrurus Garni., N. Am. E. of Rockies, Mexico ; and Crotalus L., 

 Am. (not in the W. Indies), about 11 species ; C. horridus L., common 

 rattle-snake of U.S. ; C. durissus L., to 8 ft., S.-E. U.S. ; C. terrificus 

 Laur., S. Amer. 



Sub-class 3. CROCODILIA.* 



Lizard-like long-tailed Reptiles, usually of considerable or 

 moderate size, with immoveable quadrates, a hard palate, and a 

 quadrato-jugal arch, and with teeth implanted in alveoli of the jaws 

 to which they are confined ; with loose abdominal ribs, sternum 

 and inter clavicle, a sacrum composed of two vertebrae. The ven- 

 tricle is divided by a complete septum. Anal opening longitudinal. 



Crocodiles are scaly animals, the scales consisting of cornifi- 

 cations of the epidermis. They have two pairs of limbs of which 

 the anterior have five digits, the posterior four. The three 

 preaxial digits in each limb possess nails. The hind feet are 

 more or less webbed. The nostrils are placed at the end of the 

 long snout and can be closed. The tympanic membranes are 

 exposed, but can be covered over by a cutaneous fold. The 

 eyes have vertical pupils, two lids and a nictitating membrane. 

 There is a bony plate in the upper eyelid. They all possess on 

 the back, and sometimes (Caiman, Teleosaurus, Stagonolepis} on 

 the belly, a dermal skeleton of bony plates, which are arranged 

 in transverse rows and correspond in form to the overlying epi- 

 dermal scales. The bony plates of the back are pitted and 

 sculptured and frequently keeled ; the ventral plates are less 

 sculptured, not keeled, and are sometimes composed of two 

 suturally united pieces, a small anterior and a large posterior. 

 On the tail these plates form a dentated dorsal crest, paired in 

 front, but single behind. 



The vertebral column is marked out into cervical, dorsal, 



* Cuvier, " Sur les differentes especes de Crocodiles vivants et leur 

 caracteres distinctifs." Ann. du Mus. d'hist. Nat., 10, 1807. R. Owen, 

 " Palaeontology ," London 1860. Huxley, " On the dermal armour of 

 Jacare and Caiman, etc." Journ. Proc. Lin. Soc., 4, 1860. Rathke, 

 " Untersuch. ub. d. Entwick, u. d. Korperbau der Crocodile," Braunschweig, 

 1866. Huxley, " On Stagonolepis robertsoni and on the evolution of the 

 Crocodilia," Quart. J. Geol. Soc. 31, 1875, p. 423. Id. ' Crocodilian remains 

 in the Elgin Sandstone,' Memoirs of the Geological Survey of the United 

 Kingdom, monograph hi., 1877. Cope, " Crocodilians, Lizards and Snakes 

 of N. America," Rep. U. S. Nat. Mus., 1898. Boulenger. " Catalogue 

 of Chelonians and Crocodiles in the British Museum," 1889. Hoffman, 

 Gadow. Zittel, op: cit. 



