The surface of the body of fishes is termed naked, when it is destitute of scales ; scaly, when provided with them: smooth, when the scales are without an. gles, furrows, roughness, or inequalities ; lubricous, or slippery, when invested with a mucous or slimy humour ; tuberculated, or rough, when covered with prominent warts or tubercles ; papillous, when co vered with fleshy points ; spinous, when the asperities are elongated, and pointed at their extremities ; loricated, or mailed, when the body is enclosed in a hard, cal lous, or bony integument, or in scales so closely united as to seem but one ; fa.sciat ed, or banded, when marked with trans verse zones from the back to the belly ; striped, when marked with very narrow, scattered and coloured streaks ; vitiated, when marked with longitudinal zones along the side, from the head to the tail ; reticulated, or chequered, when marked with lines forming the appearance of net work ; pointed or dotted, when marked with points, either longitudinally dispos ed, or without order; and variegated, when of different colours.
The head is always placed at the ante rior part of the body, and reaches from the extremity of the nose to the gills. The head contains the mouth, nose, jaws, lips, teeth, tongue, palate, nostrils, eyes, bran chial opercules, the branchiostegous membrane, the aperture of the gills, and the nape. The branchial opercules are scaly or bony processes, situated on both sides of the head, behind the eyes, clos ing the aperture of the gills, and sustain iu branchial membrane. The bran ,chial, or branchiostegous membrane, is a true fin, formed of cartilaginous crooked bones, joined by a thin membrane, lurk ing under the opercula, to which it ad heres, and is capable of being folded, or expanded, as necessity requires.
The trunk is that part of the body which extends from the nape and branchi al aperture to the extremity of the tail. It comprehends the gills, throat, thorax, back, sides, abdomen, lateral line, anus, tail, and scales. The gills, or branchi2e, consist, for the most part, of four crook ed, parallel, unequal bones, furnished on the outer, or convex part, with small soft appendages, like the beards of a fea ther, and generally of a red colour.
The fins consist of several rays, con nected by a tender film or membrane ; and they are raised, expanded, or moved, in various directions, by means of priate muscles. The rays of the fins are either jointed and flexible small bones, whose extremity is often divided into two parts, or hard and prickly, without division at the extremity. In some cases,
those on the back of the fish are furnish ed with membranaceous appendages, simple, or palmated, and adhering to the apex, or sides. The fins, according to their position, are denominated dorsal, pectoral, ventral, anal, or caudal.
The skeleton of a fish is the assemblage of bones which constitutes the frame work of its body. The number of these bones is not uniform in each individual, but varies according to age and species. They may be conveniently divided into those of the head, thorax, abdomen, and fins.
The muscles are an assemblage of small bundles of fleshy fibres, partly red, and partly whitish, enveloped in a common membrane. The first of these is called the fleshy portion of the muscle ; the se cond the tendon. Each muscle thus com posed is susceptible of contraction and di latation. The former is accompanied by a visible swelling, hardening, wrinkling, and shortening of the muscle, and the lat ter by its elongation, expansion, and re covery of its former softness and flexibili ty. Its force, in general, depends on the quantity of fibrous matter which enters into its composition, and its moving power on the length and size of the fibres.
The brain of fishes is a very small organ relative to the size of the head. It is di vided into three equal lobes, of which the two anterior are contiguous ; the third be ing placed behind, and forming the cere bellum. These three lob es are surround ed by a frothy matter, resembling saliva. In this region, the optic and olfactory nerves are easily discovered.
The swimming, or air bladder,or sound, is an oblong, white, membranous bag, sometimes cylindrical, sometimes ellipti cal, and sometimes divided into two or three lobes, of different lengths. It is usually situated between the vertebrae and the stomach, and included within the pe ritonxiim. In some fishes it communicates with the stomach, and in others with the oesophagus. The flat fishes are tinpro vided with this organ.
The intestines, which in man are placed transversely, have a longitudinal position in fishes, and are all connected with the substance of the liver. They are is ge neral very short, making only three turns, the last of which terminates in a common outlet or vent. The appendices, or se condary intestines, are very numerous. composing a group of worm-like proces ses, all ultimately terminating in two large canals, onenine into the first intestine. in to which they discharge their peculiar fluid. We shall, under the word PISCES, give an account of the several functions peculiar to this class of animals.