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masses, and in the several lime-stone strata : but it is very rare to 
find them possessed of either their spinous or transverse processes. 
Among those fossils which have been described as scarce, are those 
vertebrae which bear somewhat of the form of an hour-glass. These, 
however, are by no means so rare as has been supposed, the vertebrae 
of fish in general approaching to this form. 
When a longitudinal section of a series of the vertebrae of fish, im- 
bedded, 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 
vertebra. For as there is a conical cavity both in the fore and hind 
partof each vertebra, from which results, when the vertebrae areunited, 
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 con- 
tained, 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 vertebrae 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 
extremity frequently show the articulations of the small long bones 
which support the finny membrane of the tail. One of these is repre- 
sented Plate XIV. Fig. 14 ; and another, of a peculiar form, is shown 
Plate XIV. Fig. 15. 
* Phil. Trans, for 1809, p. 177- 
