VERTEBRATA : REPTILIA. 



533 



hinder pair are the xiphisternals ; while the unpaired piece is 

 termed the entosternal (fig. 292 s). The precise nature of the 

 bones of the plastron is still a matter of doubt. Some regard 



Fig. 291. Transverse section of the skeleton of Chelone midas in the dorsal region, c 

 Body of one of the dorsal vertebrae ; n Expanded spinous process or " neural plate " 

 of the same; r r Ribs ; c' c' "Costal plates;" m m Marginal plates; //La 

 eral elements of the plastron. (After Huxley.) 



Lat- 



them as wholly corresponding with the sternum or breast-bone; 

 others regard them as wholly integumentary; while others, 

 again, hold what is doubtless the correct opinion that the 



Fig. 292. Bones of the plastron of the Loggerhead Turtle (Chelone caoiianna). s En- 

 tosternal ; es Episternal ; hs Hyosternal ; ps Hyposternal ; xs Xiphisternal. (After 

 Owen.) 



plastron is formed partly of bones belonging to the endo- 

 skeleton proper and representing the sternum, in part, at any 

 rate, and partly of integumentary ossifications. 



