■^ 2 2 



CHELONIA 



CHAP. 



logous witli the interclavicle, the epi-plastra are homologous 

 with the clavicles of other Eeptiles, while the other pieces 

 are genetically derived from, and are further moditications 

 of, the so-called abdominal ribs of the Crocodilia and Prosauria, 

 These plastral plates are never in direct contact with the 



PiQ (57. — Bony shell of Tcstudo ibera. A, Ventral; B, dorsal; C, left-side view. lu 

 B, and on the right half of A, the jiosition of the horny shields is indicated by 

 dotted lines. The underlying hony plates are marked by strong lines. In B the 

 1st nenral and costal plates, the 4th neural, costal, and 6th marginal plates, and 

 the 7th neural plate are shaded. 1, 4, 6, First, fourth, and sixth neural plate ; M, 

 in C, fifth left marginal plate ; yu, nuchal plate. 



shoulder-girdle or with any other parts of the internal skeleton. 

 In the young of all tortoises, and in the adult of the Chelonidae 

 and Trionychidae, the several plastral plates enclose large, 

 irregularly-shaped fontanelles. These are more or less filled up 

 in the other groups ; and in the Testudinidae especially the 

 whole plastron forms one continuous mass. The navel is situ- 

 ated between the hyo- and hypo-plastrals. Both these pairs are 

 broader than the others, and are connected with the carapace by 



