543 ICHTHYOLOGY. 



Haddock and Cod, have three dorsals. The anal fin corres- 

 ponds to the dorsal, but is placed beneath the body, just behind 

 the vent. The principal instrument of motion is the tail fin. 

 In those fishes which swim most swiftly, the tail is forked, each 

 division being pointed, as are also the pectorals ; while in those 

 of less active or sluggish habits, the tail fin, as well as the pec- 

 torals, is commonly short, even or rounded. The rapid and 

 powerful strokes of this fin, given obliquely right and left upon 

 the water, urge the fish rapidly on in a straight course. The 

 pectorals and ventrals do not appear to be much used for com- 

 municating motion ; their chief office is to balance the body, or 

 for turning, and for rising and sinking in the water. 



Fins without distinguishable rays, or in which the rays are 

 covered with a mass of fatty matter, or else entirely absent, are 

 called adipose. A fin of this description is found on the back 

 of the Brook Trout, (Salmo fontinalis,) in the rear of the main 

 dorsal fin. 



The bones are less dense and compact in their structure than 

 those of the other Vertebrates, yet some of the Spiny-rayed 

 Fishes possess considerable hardness. In the third group, CHON- 

 DROPTERYGII, or CARTILAGINOUS FISHES, (see Chart,) which in- 

 cludes the formidable Rays and Sharks, the skeleton is com- 

 posed of gristle or cartilage instead of bone. Some of the species 

 of this order seem, however, to make an approach to the osseous 

 divisions. This is especially true, (1) of the SPOONBILL, Polydon 

 reticufatus, an extraordinary fish, two feet or more long, found in 

 the Mississippi, known at once by its snout, which is excessively 

 prolonged, very flat and lanceolate, and in length nearly equal to 

 the whole body ; (2) the COMMON or SHORT-NOSED STURGEON, 

 Acipenser (Lat. a sturgeon,) brcvirostris, which has the body 

 covered by hard bony tubercles ; (3) the Chimarida, or SEA 

 MONSTERS, so named from the fantastic shape of their heads, 

 which have a singular hoe-shaped appendage, tipped with spines 

 and somewhat-like a crest, upon their snout, (see Chart.) The body 

 of one species, Chim&ra borealis, which looks almost as much like 

 a reptile as a fish, terminates gradually in a long slender filament. 



The cone-shaped cavities of the vertebra, or joints of the spine, 

 are in the Fishes filled with a jelly-like substance, continued 

 through the whole spine, by means of a hole pierced through the 

 center of each vertebral joint. Though the tubular perforation 

 is usually small, yet in many of the gristly or cartilaginous 

 fishes, it is of so great a diameter as to reduce the vertebrae to 

 mere cartilaginous rings. 



Connected with the vertebrae above and below are spinous 



