REPTILIA 297 



642. Order I. — Rhynchocephalia are represented by a single species 

 living on islands off the coast of New Zealand. The animals are lizard- 

 like, but more primitive in a number of ways. 



643. Order 2. — The Testudinata or turtles have a very compact form 

 with bony dorsal and ventral shields, the carapace and plastron. The 

 jaws are covered with a horny sheath forming a beak. Teeth are wanting. 

 The carapace is formed by the broad dorsal spines and the much ex- 

 panded ribs together with a series of marginal plates of dermal bone. 

 The plastron is chiefly composed of plates of dermal bone. The shell is 

 covered with thick horny scales, the "tortoise shell." Most of the 

 Testudinata are aquatic. Snapping turtle, terrapin, tortoise, and sea 

 turtles. 



644. Order 3. — The Emydosauria are large aquatic lizard-like reptiles. 

 The alligator, crocodile and gavial are well known. There are only a 

 few genera. The skin contains bony plates as well as horny scales. The 

 teeth are set in sockets. The ventricle is completely divided into two 

 chambers. 



645. Order 4. — The Squamata comprise both lizards and snakes. 

 Usually the lizards have two pairs of appendages while the snakes have 

 none, but among the lizards are found various stages of degeneration of 

 the appendages even to forms in which no evidence of limbs is discernible 

 externally. On the other hand among snakes rudiments of appendages 

 are also found. The Squamata are distinguished from the other reptile 

 orders by the movable quadrate bone. In the sub-order Lacertilia, the 

 lizards, the upper jaws are not movable. The tongue is flat. There is 

 a urinary bladder. In the sub-order Ophidia, the upper jaw is movable, 

 the tongue is forked and enclosed in a sheath and there is no bladder. 

 The ear drum and middle ear are also wanting. Another small sub- 

 order of lizard-like forms, including the chameleon, are tree dwellers and 

 as a special adaptation to such conditions the toes are opposable for clasp- 

 ing, and the tail is prehensile. 



646. Class V. Aves. — The Birds are in many respects the 

 most highly specialized of all animals. The feathers, which 

 are characteristic of the class, are specialized epidermal struc- 

 tures and are very remarkable. The skin is comparatively thin 

 but the feathers more than compensate as protective structures. 

 For resistance to mechanical injury, or protection from cold, 

 or heat, or wetting, or adaptation to thermal control, or for the 



