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
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