162 Dr. J. E. Gray on the Development and Cohesion 



T. scabra of Latreille, which is figured here under the name 

 of Rhinoclemmys scabra. Mr. Owen figures the skeleton of 

 a young Testudo indica '■ Phil. Trans.' cxxxix. 1849, t. 19. 

 f. 4-6. These are the only observations I have noticed on 

 the form of the bones in the sternum of the young Chelonians. 

 These authors did not seem to be aware of the great variation 

 in the forms of the bones in the young of the diiferent genera, 

 the changes that they undergo during the growth of the animal, 

 and the important assistance that their study affords in the 

 arrangement of the animals. 



Land-Tortoises (Testudo). 



The bones of the sternum in young Land-Tortoises ( Tes~ 

 tndo) are the same in number as in the Terrapins, but of very 

 different form. The front two pairs and the hinder two pairs 

 each form a very distinct group, separated by a more or less broad 

 space across the middle of the sternum. The front pair of bones 

 are generally large and well developed, and the odd bone on 

 the inner side of them is triangular and usually small. The 

 two lateral pairs are somewhat similar, broad and expanded, 

 and more or less semilunar, each pair having a convex semi- 

 circular edge towards the middle of the inner central vacant 

 disk. The hinder pair are attached to the inner side of the 

 outer edge of the hind lateral pair, and are generally united 

 together. 



This formation is well exhibited in a specimen of Testudo 

 tabidata (PI. IV. fig. 1) 2\ inches long, and also in a specimen 

 of T. elei^hantopus (PI. IV. fig. 2), about 4 inches long, and 

 Testudo radiata^ 1\ inches. The lateral bones in Testudo 

 radiata and in T. indica are much more convex and irregular 

 on the edge towards the centre of the sternum. 



In T. 'platynota (PI. IV. fig. 3), about 2 inches long, the 

 lateral bones are of the same lunate shape as in T. tahulata^ 

 but the lateral pair are much further apart. Perhaps this 

 arises from the ossification being less developed. The lateral 

 bones in T. semiserrata^ about 2 inches long, are similar to 

 those of the young T. tabulata, but rather more irregular 

 in their outline ; but the opposite bones are rather further 

 apart, leaving a broader central space between them than in 

 T. tabidata. 



These bones evidently enlarge in size, their edges approxi- 

 mate, and at length join and coalesce. Thus T. stellata 

 (PI. IV. fig. 4) appears to become solidified when of a very 

 small size ; for in a specimen only 2 inches long the ribs are 

 dilated and ossified nearly to the margin, and the sternal bones 

 are very expanded, forming a nearly solid disk, leaving only 



