126 



PLASTRON OF THE TURTLE, 



ceeding neural plates have the same relations with the 

 succeeding neural spines; the rest are independent der- 

 mal bones. The costal plates of the carapace are super- 

 additions to eight pairs of the pleurapophyses or ver- 

 tebral portions of the second to the ninth ribs inclusive. 

 The slender or proper portions of these ribs project 

 freely for some distance beyond the connate dermal 

 portions, along the under surface of which the rib may 

 be traced, of its ordinary breadth to near the head, which 

 liberates itself from the costal plate to articulate to the 

 interspace of the two contiguous vertebra, to the pos- 

 terior of which such rib properly belongs. 



The plastron, or floor of the bony house, consists in 

 the genus Chelone^ as in the rest of the order, of nine 



Fig. 22. 



PLASTRON OP CHELONE CAOUANNA. 



pieces — one median and symmetrical, and the rest in 

 pairs. With regard to the homology of these bones, 



