264 



When a longitudinal section of a series of the vertebrae of fish, imbed- 

 ded, for instance, in lime-stone, is made, a series of bodies are seen, 

 bearing the hour-glass form, each being the section of a body of a ver- 

 tebra. For as there is a conical cavity both in the fore and hind part 

 of each vertebra, from which results, when the vertebrae are united, a 

 series of cavities bearing the form of two cones united at their base ; so the 

 body of each vertebra, narrowing to its centre, presents, by a longitudinal 

 section, a surface which, in its longitudinal direction, bears the form of 

 a longitudinally-divided hour-glass. It is in these cavities, formed by the 

 union of the vertebrae, that the fluid is contained, which, according to 

 the observations of Mr. Home, being incompressible, preserves a proper 

 interval between the vertebrae, to allow of the play of the lateral elastic 

 ligaments, and forms a ball round which the concave surfaces of the ver- 

 tebrae are moved, and which readily adapts itself to every change which 

 takes place in the form of the cavity *. 



Among the Shepey fossils are sometimes found the last vertebrae of the 

 tail. These are flat and of a triangular shape, and at their widest extre- 

 mity frequently show the articulations of the small long bones which 

 support the finny membrane of the tail. One of these is represented 

 Plate XIV. Fig. 14 ; and another, of a peculiar form, is shown Plate XIV. 

 Fig. 15. 



* Phil. Trans, for 1809, p. 111. 



