STRUCTURE OF FISFTE^ 81 



caudal portion of the spine, it is directed downwards, and often 

 forms, with its fellow of the opposite side, a ring 1 , from the lower 

 part of which arises a long spinous process, similar to that which 

 is situate on the dorsal face of the vertebra. 



11. The ribs are sometimes wanting; at other times, they 

 encircle the whole abdomen, and, in a small number of fishes, 

 they are fixed to a series of unpaired or single bones, which 

 should be regarded as the sternum. They frequently sustain 

 one or two stylets which have an outward direction, and pene- 

 trate the flesh. Sometimes there are similar stylets arising from 

 the bodies of the vertebra, and hence it is that, in certain genera, 

 such as herrings, fish-bones become so numerous. 



12. On the middle line of the body, we also find a certain 

 number of bones, called intvrtpiiwl, (Fig. 43, /.; which gene- 

 rally rest upon the ends of the spinous processes of the vertebrae, 

 and, by their opposite ex- , v .. 



tremities, articulate with the 

 rays of the middle fins, (//.) 

 These rays are sometimes 

 pointed bones, called stiuys, 

 or spines ; sometimes they 

 are stalks or stems bony 

 only at the base, formed of 

 a multitude of small articu- 

 lations in continuation, and INTKRSPINAI. BONES. 

 often branched towards the end. These last appendages are 

 called ,vo/>, or articulated rays: they always form the caudal 

 fin, and sometimes there are no others. 



13. The lateral fins, which represent the extremities, are 

 terminated by rays similar to those of the vertical fins, and 

 analogous to fingers. At the base of the pectoral fin we find a 

 series of from four to five small flat bones, comparable to the 

 bones of the carpus, which, in their turn, are attached to two 

 flat bones which seem to be the radius and ulna enlarged This 

 apparatus is supported on a species of bony belt, situate imme- 

 diately behind the gills, and on which the operculum applies: it 

 consists of a series of three bones, extending from the cranium 

 to the hyoid apparatus, and supports posteriorly a long stylet. 

 The principal piece that enters into its composition is that which 

 supports the fore-arm, which may be compared to the humerus, 

 (See Fig. 42, 1'aye 80.) : it joins below with that of the opposite 



11. What are the characters of the ribs ? 



12. What are the interspinal bones ? What are the rays of the fins ? 



13. What parts of fishes represent the extremities of mammals ? 



