SKELETON 



315 



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 



FIG. 61. Various plastra arid their horny shields. 1, Testudo ibera ; 2, Macroclemmys 

 temmincki ; 3, Cinosternum odoratum ; 4, Sternothaerus nigricans ; 5, Chelodina 

 longicollis ; 6, Chelone mydas. a or an, Anal shield ; abd, abdominal shield ; f or 

 fern, femoral ; g or gul, gular, unpaired in Fig. 3 ; h or hum, humeral shield ; i or 

 int.g, intergular ; im, infra-marginals ; in, marginals ; p orpect, 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 the centrum, are much reduced, sometimes to mere 

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

 pair of ribs, in many cases without reaching the carapace. The 

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

 are intimately involved in the formation of the first to seventh 

 costal plates. The ribs of the two sacral vertebrae sometimes 

 remain quite distinct throughout life, just touching the upper 



