ROOM III. VERTEBRA OP REPTILES. 163 



data. It is only by a strict regard to truth, and the substi- 

 tution of facts for hypotheses, that the science of Palaeontology 

 can be extended, and its principles securely established. 



From the great number of vertebrae in many reptiles, 

 amounting in the individuals of some species to nearly two 

 hundred, these bones are, perhaps, the most abundant of all 

 the fossil relics of this class of animals. In many deposits, 

 the vertebrae are almost always deprived of their processes, 

 the body or centrum alone remaining, (as in Lign. 35, fig. 8). 

 In other strata, entire series, with the processes more or less 

 perfect, and in connexion with other parts of the skeleton, 

 are found imbedded ; as in the beautiful specimens of Ichthyo- 

 sauri and Plesiosauri in the lias limestones and shales. 



As vertebrae, or their detached processes, are frequently 

 the only vestiges of peculiar types of extinct saurians, a few 

 explanatory remarks are necessary to enable the reader to 

 appreciate the interest and importance of some of the speci- 

 mens in this collection, which are apparently but of very 

 little value. 



The bones composing the spine are designed to form a 

 flexible column of support to the trunk, and afford protection 

 to the great nervous chords constituting the spinal marrow, 

 and which extend from the brain to the tail, giving off nume- 

 rous lateral branches in their course, and conferring sensation 

 and motive power to every part of the body. To effect this 

 purpose, the upper part of each vertebra consists of a ring, 

 called the annular part or neural-arch, which is composed of 

 two processes (Lign. 35, &.), arising from each side of the 

 body, or centrum (Lign. 35, a.), with which they are connected 

 by suture, and these unite above into a solid piece, termed 

 the spinal process (Lign. 35, d). On each side of the annular 

 part there is a transverse process, (Lign. 35, e f e.), for the 

 attachment of muscles ; and, in some reptiles, as the Croco- 

 diles, the ribs are articulated to these processes. 



The vertebrae of the tail have, in addition to the above 

 apophyses, an inferior spinous process, termed the chevron- 

 bone (Lign. 35, jig. 2 and 3, /), which supports the inferior 

 layers of caudal muscles, and is articulated to the inferior 

 margin of the body of the vertebra, either by two distinct 

 heads, or by the confluence of the two laminae into a single 

 tubercle, (as in fy. 2) ; in either case an interspace is left 



