286 



VERTEBRATES I REPTILES. 



head is cut off. The muscles preserve their irritability 

 for a considerable time after being severed from the body, 

 and even the heart pulsates for hours after it is removed ; 

 nor does its loss prevent the animal from moving about. 

 The vertebrae of Reptiles are convex at one end and con- 

 cave at the other ; and their teeth, when set in sockets, 

 never have more than one prong. 



This Class comprises three Orders, Testudinata or 

 Turtles, Sauria or Lizards, and Ophidia or Serpents. Some 

 writers also include the Batrachians in this group. 



Fig. 151. 



SUB-SECTION I. 



THE ORDER OF TESTUDINATA, OR TURTLES. 



THE Order of Testudinata comprises scaly reptiles 

 which have a continuous shield upon the back, called 



carapace, which is connected 

 by bridges to another shield 

 below, called plastron, the 

 whole forming a hard cover- 

 ing for the soft organs of the 

 body. This hard covering 

 is formed of the greatly ex- 

 panded ribs and sternum, to- 

 gether with ossified skin. 

 The head, neck, and tail are 

 the only movable parts of the 

 spinal column. The jaws are 

 covered with a horny sub- 

 stance, and destitute of true 



Skeleton of a Turtle, plastron removed. teeth J tongUC short, thick, 

 cv, cervical vertebrae ; pk, phalanges ; c, and COVCrcd with fleshy fila- 



ments ; nostrils anterior, and 



, . , -, , i i 



lids ; and lungs large, and 



bone ; dv, dorsal vertebrae ; /, pelvis ; f, near together J CyCS with three 

 femur ; if, tibia and fibula ; is, tarsus ; 



, phalange, 



