J_HE REPTILES are oviparous or ovoviviparous vertebrate animals with 

 red, cold blood, with three cavities of the heart, breathing- by lungs either 

 during the whole period or, at least, in the later stages of their growth. 

 They are naked ; but frequently the skin shows scale-like folds, or is tuber- 

 cular, or forms osseous scutes. 



First Subclass. REPTILIA PROPER. 



Only one ventricle of the heart, incompletely divided ; two atria. Never 

 possessing branchiae at any period of life. One occipital condyle. Skin with 

 scale-like folds, or tubercular, or forming osseous scutes. 



This Subclass comprises the Order of Tortoises (Chelonia), p. 1, that of Lizards (Sauria), 

 p. 56, and that of Snakes (Opiiidia), p. 163. 



THE ORDER OF TORTOISES— C/^^Z0A7.^. 



T'he Tortoises we Reptiles witli the bones of the thorax united into a 

 carapace. 



The shell of the Tortoises is formed by an osseous structure covered over with an epider- 

 moid coat. The bones participating in the formation of the shell are the vertebrae, the ribs, 

 and the sternum, which are so dilated that their edges form sutures with those of the 

 neighbouring bones. In some freshwater and marine tortoises, and in young individuals, 

 large interspaces between the ends of the ribs and between the sternal bones are, or remain, 

 cartilaginous. We distinguish in the shell of a Tortoise the upper part, which is more or 



B 



