CIIELONIAN REPTILES. 323 



brae, and to allow of motion only in those of the neck, and 

 of the tail. The former, accord ini»;ly, are all anchylosed to- 

 gether, leaving, indeed, traces of their original forms as se- 

 parate vertebrae, but exhibiting no sutures at the place of 

 junction. The canal for the spinal marrow is preserved, as 

 usual, above tlic bodies of these coalesced vertcbric, and is 

 formed by their united leaves; the arches being completed 

 by the spinous processes. But these processes do not ter- 

 minate in a crest as usual; they are farther expanded in a 

 lateral direction, forming flat pieces along the back, which 

 are united to one another by sutures, and which are also 

 joined to the expanded ribs, so as to form the continuous 

 plane surface of the carapace. The transverse processes of 

 the vertebrae are well marked, but, though firmly united to 

 the ribs, do not give rise to them; for the ribs, which are 

 flattened and expanded, so as to touch one another along 

 their whole length, are inserted below, between the bodies 

 of every tvvo adjoining vertebras; while above, they are 

 united by suture with the plates of the spinous processes. 

 This change in the situation of the ribs is the consequence 

 of the change in their oflice. When designed to be very 

 moveable, we find them attached either to the extremities of 

 the transverse processes, or to the articular surfaces of a sin- 

 gle vertebra; but where solidity and security are aimed at, 

 they are always inserted between the bodies of two verte- 

 brae. This we shall find to be the case also in birds, where 

 the bones of the thorax are required to be immoveable. It 

 is remarkable, indeed, that a great number of the peculiari- 

 ties which distinguish the conformation of the chelonia from 

 that of other reptiles, indicate an approach to the structure 

 of birds; as if nature had intended this small group of ani- 

 mals to be an intermediate link of gradation to that new and 

 important type of animals destined for a very diflerent mode 

 of existence. 



The sterno-costal appendages, which connect the ribs to 

 the sternum, are, in most animals, cartilaginous: thougli oc- 

 casionally we find them partially ossified. In the tortoise, 



