THE SKELETON OB 1 THE TURTLE. THE CARAPACE. 215 



respectively the gular, humeral, pectoral, abdominal, 

 femoral, and anal, the gular being the most anterior. In 

 front of the gular shields is an unpaired intergular, and 

 the shields of the plastron are connected laterally with those 

 of the carapace, by five or six pairs of rather irregular infra- 

 marginal shields. Smaller horny plates occur on other parts 

 of the body, especially on the limbs and head. 



Two other sets of structures belong also to the epidermal 

 exoskeleton, viz. (a) horny beaks with denticulated edges 

 which ensheath both upper and lower jaws, (b) claws, which 

 as a rule are borne only by the first digit of each limb. 

 Sometimes in young individuals the second digit is also clawed. 



6. The dermal exoskeleton is strongly developed, and 

 is combined with endoskeletal structures derived from the ribs 

 and vertebrae to form the carapace. 



The Carapace (fig. 36) consists of a number of plates 

 firmly united to one another by sutures. They have a very 

 definite arrangement and include : 



(a) the nuchal plate (fig. 36, 1), a wide plate forming 

 the whole of the anterior margin of the carapace. It is 

 succeeded by three series of plates, eight in each series, which 

 together make up the main part of the carapace. Of these 

 the small 



(b) neural plates 1 (fig. 36, A, 2) form the middle series. 

 They are closely united with the neural arches of the under- 

 lying vertebrae ; 



(c) the costal plates 1 (fig. 36, A, 3) are broad arched 

 plates united to one another by long straight sutures. They 

 are united at their inner extremities with the neural plates, 

 but the boundaries of the two sets of plates do not regularly 

 correspond Each is united ventrally with a rib which pro- 

 jects beyond it laterally for some distance ; 



1 Another view commonly held is that the neural and costal plates are 

 respectively formed by the expanded neural arches and ribs. 



