BONES OP THE TRUNK OF FISHES. 7 



other caudal (Fig. 346) ; for here there is neither neck nor 

 sacrum. The body of the vertebrae has a peculiar form, being 

 hollowed before and behind into a conical cavity ; these two 

 cavities sometimes unite in such a manner, as to form a con- 

 tinuous passage ; and the double conical cavity, which is formed 

 when two vertebrae are placed together, is filled with a soft sub- 

 stance. The ring destined for the passage of the spinal marrow 

 is surmounted by a spinous process ; and on each side there is 

 generally seen a transverse process more or less distinct, which, 

 beneath the abdominal cavity, extends outwards, and is usually 

 united with the corresponding rib ; but which, in the caudal 

 portion of the column, is directed downwards, and often forms 

 with that of the opposite side a ring, from the lower part of 

 which arises a long spinous process, similar to that which is 

 situated on the dorsal side of the vertebrae. The ribs are some- 

 times entirely absent ; at other times they surround the abdo- 

 men, and amongst a small number of Fishes they are joined to a 

 series of single bones, which ought to be considered a sternum. 

 They often bear one or two pointed projections, which are 

 directed outwards, and penetrate into the muscles. There are 

 also, sometimes, similar processes, which spring from the bodies 

 of the vertebrae ; and it is thus that, in some tribes, such as 

 amongst the Herrings, the small bones of Fishes become very 

 numerous. Lastly, we find on the central line of the body a 

 number of bones, termed interspinous (Fig. 350), which are 

 usually applied against the extremities of the spinous processes 



of the vertebrae, and which 

 articulate at their opposite 

 ends with the rays of 

 the median fins. These 

 rays are sometimes pointed 

 bones, which are then term- 

 ed spines: but they are 

 sometimes ossified only at 



F.o. 350.-DOR8AL Fm, supported on spiny rays, the j r ^ the remainder 



, r, and these resting on interspinous bones, 1. 1. 



being formed of a series 

 of little cartilaginous pieces, jointed together ; and often branch- 



