SKELETON OF FISHES. 415 



behind, (considering the spinal column as ex- 

 tended horizontally), so as to form cup-like 

 hollows : by which means, where the concave 

 surfaces of two adjacent vertebrae are applied to 

 one another, a cavity, having the shape of a 

 double cone, is formed by the junction of the 

 margins of these conical hollows. These cavi- 

 ties are distinctly seen laid open in Fig. 188, 

 which represents a vertical section of three 

 adjacent vertebras of a cod. The edges that are 

 in contact, are united all round by an elastic 

 ligament, which readily yields to the bending of 

 the vertebrae upon one another by the applica- 

 tion of any force to one side of the spine, and 

 restores it to its former state when the force has 

 ceased to act. The extent of motion in each 

 joint is but small ; but being multiplied in the 

 whole series, the resulting effect is considerable. 

 The cavity itself is filled with a gelatinous, but 

 incompressible fluid substance, which constitutes 

 a spherical pivot for all the motions of the joint. 

 This singular kind of articulation would ap- 

 pear framed with a view to allow of motion in all 

 directions. Here, however, the motions are 

 restricted by the extension of the spinous pro- 

 cesses (s, s, in the preceding figures), which in 

 fishes are of great length ; so that they effec- 

 tually prevent all flexions either upwards or 

 downwards, and limit it to those from side to 

 side. It is precisely these latter kind of motions 



