IX 



SKKI.KTON 



15 



remarkable to a purely neural attachment. In all the Chelonia 

 the ribs are devoid of the tubercular portion. 



The cervical vertebrae have no ribs, except mere traces in the 

 shape of small nodules. On the tail the ribs are often large, and, 

 when fused with their neural supports, look like transverse 

 processes ; the whole arrangement exactly resembles that of 

 Crocodilia. The first pair of thoracic ribs, those borne by the 



£/nlars 



Fig. 61. — Various plastra ami their hoiiiy shields. 1, Testuilo ihera ; 2, Macroclemmys 

 temmincki ; 3, Cmosternum odoratmn ; 4, Slernothaerus nigricans; 5, Chelodina 

 lonf/icollis ; 6, Chelone mydas. a or an, Anal shield ; abd, abdoiiiiual shield ; / or 

 fein, femoral ; g or gul, gular, impaired in Fig. 3 ; A or hum, humeral shield ; i or 

 int.g, iutergular ; im, infra-marginals ; in, marginals ; p ov ped, pectoral ; x, in Fig. 

 1, inguinal shield constituting, with the axillary xx, the last trace of infra- 

 marginals. 



ninth vertebra, are peculiar. They arise from the anterior 

 portion of tlie centrum, are much reduced, sometimes to mere 

 threads of bone, and lean against the anterior rim of the second 

 pair of ril)S, in many cases without reaching the carapace. The 

 next following ribs, those of the tenth to the sixteenth vertebra, 

 are intimately involved in tlte formation of the first to seventh 

 costal plates. The ribs of the two sacral vertebrae sometimes 

 remain quite distinct throughout life, just touching the up]>er 



