476 



FISH. 



have processes both upwards and downwards, some- 

 thing in the form of a double comb, while the former 

 have only spinous processes on the dorsal edge, and 

 lateral processes on each side, which form the com- 

 mencement of the walls of the cavity of the fish, pro- 

 tect a great or systematic artery, and in those species 

 which fiave the ribs generally attached to them, 

 the section of this column is sometimes cylindrical, 

 sometimes angular, and sometimes compressed or 

 flattened in the direction of the mesial plane. In 

 bony fishes, each vertebra is composed of two hollow 

 cups, of a conical form, the cavities of which are filled 

 with fibrous cartilage ; and in many species this car- 

 tilage extends through the centre of the column in 

 one continuous cord for its whole length. The spinal 

 marrow is not, as in land animals, contained within 

 the vertebral column, but lies along the upper side of 

 it, passing through the bases of the dorsal processes, 

 which are all double at their origin, and may gene- 

 rally be split for their whole length. When the car- 

 tilaginous substance which unites the vertebrae or 

 pieces of the back bone is examined, it has the ap- 

 pearance of a series of concentric rings ; and it has 

 been alleged that the number of these answers to the 

 number of years that the fish has lived, but of this 

 there is no proof. 



The ribs of fishes vary much ; cartilaginous ones 

 have no true ribs, and in the bony fishes they are 

 simple, forked, or double. In the carp family they 

 are flat, in the cod family round, and in the herring 

 they are like bristles. The number of ribs, and also 

 of vertebrae, are good characters in distinguishing the 

 several species offish. 



Besides the parts already mentioned, the only 

 portion which can be regarded as directly connected 

 with the skeleton, is the bony structure of the shoulder, 

 or that which supports the pectoral fins. These con- 

 sist of the two arches which, in fishes that have 

 regular gills, always support the posterior edges of 

 them, and furnish a place of resistance against which 

 the gill-lids close, as well as give security to the anterior 

 part of the cavity of the body. When perfect, these 

 arches are united at their under extremities by car- 

 tilage, and at their upper ones they are attached to 

 the vertical column, to the posterior part of the 

 cranium, or to both. To these arches are attached, 

 not by regular joints but by cartilaginous unions, the 

 bones of the pectoral fins, which usually consist 

 of two pieces, answering to the arnVand fore-arm, 

 and some small bones at the extremities of the latter, 

 which have some analogy to the bones of the wrist. 

 To these last the rays of the pectoral fins are at- 

 tached. The boner, which support the dorsal and 

 anal fins are generally detached pieces, included in 

 the flesh, though in some instances the dorsal is 

 joined to the processes of the spine, and more rarely 

 the anal to the same. When the ventral fins are 

 situated as far forward as the pectorals, or farther, they 

 are connected with the same bones, sometimes through 

 the medium of an imperfect sternum or breast bone. 

 When the ventrals are situated farther in the rear, 

 the bones to which they are attached are most com- 

 monly imbedded in the flesh, without any connexion 

 with the vertebral column. 



The bones of the head are so many and com- 

 plicated, and they vary so much in different species, 

 that they cannot easily be made the subject of popular 

 description. The bones of the jaws are generally 

 very distinct from those of the cranium, and admit of 



separate motions, and there are peculiar bones in the 

 pharynx at the back of the mouth. The bony arches 

 which support the gills are attached at one ex- 

 tremity of the os hyoides. The gill-lid consists of 

 several plates of thin bone, which, in the fishes which 

 have free gills, have a good deal of motion, and by 

 expelling the water when they close, not only per- 

 form an office in respiration similar that of the raising 

 of the diaphragm in the mammalia, bnt also, by the 

 force with which they throw the ejected water back- 

 wards, assist in the progressive motion of the fish. 



We have already mentioned that the bones of 

 fishes are, generally speaking, of more flexible con- 

 sistency than those of land animals, and contain pro- 

 portionally less of the salts of lime. Their base of 

 animal matter is different from that of the mammalia, 

 as it does not appear that they contain much, if 

 any, gelatine. Their composition has not been de- 

 termined by any very accurate analysis ; but it should 

 seem that they are so far intermediate between the 

 bones of land animals and insects, such as those of 

 crabs and lobsters, for they contain a portion of sub- 

 carbonate of lime as well as of phosphate, only the 

 quantity of the latter is more abundant. The bones 

 of some fishes undergo a very remarkable change of 

 colour when they are boiled ; thus the bones of the 

 blenny become green, or rather, perhaps, they are 

 green without any boiling, as is the case with those 

 of the gar-fish (Belone), which has also often been 

 alleged to turn grass green in boiling, whereas it is 

 green whether boiled or not, only the bones of fishes 

 are seldom objects of common observation till they are 

 boiled. 



Protecting organs. Under this name we do not 

 mean to include only those means of defence which 

 fish have against their enemies ; but their general 

 means of protection against the macerating influence 

 of the element in which they live. These may be 

 divided into the three distinct processes of skin, 

 scales, and spines. 



The skin consists of three distinct parts, a true 

 skin immediately over the muscles, a mucous tissue, 

 and an epidermis or cuticle. In those species which 

 have no scales, or very small ones, the true skin is 

 often very thick, while in those which have the scales 

 large it is often a very thin membrane. It adheres 

 much more closely to the flesh than in any other of 

 the vertebrated animals. When thick it contains a 

 great quantity of gelatine, and as such it is useful as 

 food, as glue or size, and for many other purposes. 

 The skins of the cod and eel are instances. The 

 skins of fishes have none of those villi or papilla; 

 which are found on the skins of the land vertebrata, 

 and which are generally supposed to be organs of a 

 sense of touch, and hence it has been supposed that 

 fishes have little feeling of this sense. This is, how- 

 ever, to a very great extent hypothetical ; for even in 

 land animals these papillae are by no means the most 

 delicate organs of this supposed sense of touch, for 

 they are in all probability excelled by the whiskers of 

 nocturnal beasts of prey, the margins of the wings of 

 bats, and the fine and filmy terminations of the fea- 

 thers of nocturnal birds. It is very doubtful if there 

 be any such thing as an organ of touch per se in any 

 part of the integuments in any animal; and the more 

 rational view of the case is that the feeling is in the 

 muscle, and the only office which the external integu- 

 ment performs is that of readily transmitting to that 

 any impression made on itself. Every schoolboy who 



