THE ANNALS 



AND 



MAGAZINE OF NATURAL HISTORY. 



[FOURTH SERIES.] 

 No. 63. MARCH 1873. 



XIX. — On the Original Form^ Development^ and Cohesion of 

 the Bones of the Sternum of Chelonians ; loith Notes on 

 the Skeleton of ^^\iSiYg\Q. By Dr. J. E. Gray, F.R.S. &c. 



[Plates IV., v., & VI.] 



It has long been known that the sternum of all Chelonians is 

 formed of four pairs of bones with an odd one, which is always 

 attached to the centre of the inner edf^e, opposite the suture 

 between the front pair. In some Chelonians these bones 

 always remain of nearly the same form, and are more or less 

 separate from each other during the whole life of the animal. 

 In the land Tortoises and the freshwater Tortoises or Terrapins 

 the bones of the young become expanded as the animal grows, 

 coalesce, and at length form in the adult animal a single bony 

 disk. 



Cuvier, in his chapter on the " Osteologie des Tortues," in 

 the Oss. Foss. v. p. 204, observes : — 



" Dans les tortues de terre et d'eau douce, et dans les chd- 

 lydes, ils ne laissent de vides entre eux que dans le premier 

 age seulement, ou ils se forment de rayons osseux dirigds en 

 divers sens dans le disque encore cartilagineux du plastron, 

 comme les os du crane dans les fetus des mammif^res ; mais 

 avec l'S,ge ces rayons se joignent de toute part et forment un 

 disque compact dans toutes ses parties et qui s'unit par une 

 ^tendue plus ou moins considerable de chaque c6i6 au bouclier 

 dorsal. Voyez pi. xii. f. 44, le plastron d'un jeune Testudo 

 scahray 



The sternum figured is very like that here figured as belong- 

 ing to Emys concentrica, and is quite different from that of 



Ann. & Mag. N. Hist. Ser. 4. Vol. xi. 11 



