242 PALEONTOLOGY. 



are compact, and in thickness about one-sixth of the diameter 

 of the bone. The terminal neural arches support each a low 

 median ridge or rudimental spine, which soon subsides. The 

 trace of neural canal in like manner disappears, or is continued 

 by tw T o distinct slender canals which traverse for a certain 

 extent the substance of the thicker upper wall of the cavity 

 of the vertebral body. A single large vascular canal opens on 

 the wider surface midway between the two ends of the body. 

 There is no trace of transverse processes, rib-surfaces, or 

 haemapophyses ; this, and the absence of the continuous 

 neural canal, indicate these singular vertebrae to belong to 

 the tail. From the long caudo-vertebral style of anourous 

 Batrachia the vertebras of Tanystrophceus differ in having dis- 

 tinct articular surfaces at both ends. The difference of shape 

 and size in the few that have been found also indicates that 

 there were more than two such vertebrae in the tail of the ex- 

 traordinary animal to which they have belonged. Caudal 

 vertebrae of the normal proportions and structure, from 

 muschelkalk of the same localities with Tanystrophceus have 

 been referred to Nothosaurus. It is possible, however, that 

 one or other of the remarkable genera — Simosaurus, Placodus, 

 e.g. — may have possessed the peculiar structure in the tail, 

 or some part of it, which the tanystrophaean vertebrae indicate. 

 The first four vertebrae of the neck or trunk of the Fistularia 

 tahaccaria are those which most resemble in their proportions 

 the vertebrae above described ; but none of the fistularian 

 vertebrae have the articular concavity and the zygapophyses 

 at both ends ; the first presents them at the fore end, and the 

 last at the hind end, and the modifications of both these 

 finished articular ends pretty closely correspond with those of 

 Tanystrophceus ; but the second and third vertebrae of Fistu- 

 laria are united with the first and fourth by sutural surfaces 

 with deeply-interlocking pointed processes. 

 Genus Sphenosaurus. 



