2o6 Elementary Zoology, 



supported, however, by the elongated digits. Some were tooth- 

 less, and appear to have possessed beaks. 



6. Testudinata. — The tortoises and turtles have the well- 

 known and characteristic " shell," which is formed by bony 

 plates, partly formed by the flattened neural spines and ribs 

 and other bones. Covering this is a horny set of plates, which 

 are epidermic in structure. This character absolutely distin- 

 guishes the Testudinata. 



7. Lepidosmiria. — This group includes both the lizards and 

 snakes, which are by some made the representatives of two 

 equivalent orders. They agree in the covering of epidermic 

 scales. The teeth are fused to the jaws, and not implanted in 

 distinct sockets. The cloaca opens transversely, and there is a 

 double penis. In both the limbs may be more or less unre- 

 presented ; and these are the only reptiles in which the teeth 

 are sometimes grooved or perforated for the poison-glands 

 (= modified salivary glands). The Gila monster {Heloderma) 

 and an Oriental form are poisonous lizards ; while' there are, 

 of course, numerous poisonous snakes. The snakes are separable 

 from the lizards by the incompletely united rami of the lower 

 jaw, which thus permits the swallowing of larger prey ; they 

 have no urinary bladder, while the lizards have one. Snakes 

 are more constantly apodous. 



8. Rhytichocephalia. — This group is represented at the 

 present day by only a single lizard-like animal, the Hatteria, or 

 Sphenodon, of New Zealand islands. The skull differs in 

 several points from that of the lizard's, and the body is pro- 

 vided in addition to the true ribs with abdominal ribs, also 

 found in the Crocodilia. Some of the ribs bear uncinate 

 processes, as in birds. 



9. Crocodilia. — These are the most highly organized of 

 living reptiles. The heart is completely four-chambered. The 

 skin has not only epidermic scales, but bony mesodermic 

 plates beneath them in many parts of the body. The teeth 

 are in distinct sockets. The ribs may possess uncinate pro- 

 cesses, and, as already said, there are abdominal ribs. The 

 cloaca has a longitudinal opening, and the penis is single. 



Sub-class 5. Aves. — By many the birds are placed in one 



