ICHTHYOLOGY, 



667 



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Structure he gives an account of five rare species of British fish- 

 es, to be afterwards taken notice of. The second pa- 

 " per is from the pen of the secretary, Mr Neill. It 

 ^ __- contains a list of the fishes of the Forth, and the lakes 

 and rivers in the neighbourhood of Edinburgh, which 

 have been observed by the author. The species amount 

 to 76 in number, and among these there is one new Bri- 

 tish species. 



The last author whom we shall mention as having 

 contributed to extend our knowledge of the distribution 

 of British fishes, is the late Rev. George Low, minister 

 of Birsa and Hara. The Fauna Orcadentir, which he 

 left behind him in MS. was published in the year 1813, 

 and contains an extensive list of the fishes which the 

 author observed in the seas around the islands of Ork- 

 i;i \ . 



CHAP. II. 

 STECCTURC AND FUNCTIONS OF FISHES. 



As fishes are destined to live in water, we may ex- 

 pert to find all their organs constructed in such a man- 

 ner, as to accommodate themselves to the properties of 

 that element. We propose to examine these organs in 

 succession, and to bestow attention at the same time to 

 the functions which they perform. By treating the 

 subject in this manner, repetitions will l>c avoided, and 

 the general reader assisted in comprehending the eco- 

 nomy of this important class of animated beings. 



SECT. I. Organt of Support. 



TUB bones of fishes vary in form, proportion, and 

 number, according to the species. The skeleton is more 

 complicated than that of man, and is difficult to prepare 

 and preserve. Hence the osteology of fishes is a sub- 

 ject but little attended to by naturalists. Avoiding all 

 minute details, we propose to consider the skeleton, as 

 consisting of a cranium, spine, and ribs. 



As the cranium of fishes is covered with skin only, its 

 form is easily ascertained, and it exhibits remarkable 

 differences in shape according to the species. In all the 

 species it is large in proportion to the size of the body. 

 The cranium of osseous fishes consists of a great num- 

 ber of separate pieces. These amount to eighty in the 

 perch. But as these bones are soon ossified together, 

 it becomes very difficult to trace the original lines of 

 separation in aged individuals. The occiput appears 

 like a vertical truncation of the cranium, and is united 

 to the pine by a single tubercle placed below the fora- 

 men. The motion of the head is very limited in every 

 direction. In some of the cartilaginous fishes, the head 

 is joined to the vertebral column by two condyles ; but 

 this articulation is equally incapable of extensive mo- 

 tion as the former. 



The vertebral column is either cylindrical, angular, or 

 compressed. The vertebne may readily be distinguish- 

 ed from those belonging to the higher classes, by the 

 peculiar form which they exhibit. The body of the 

 vertebra is of a cylindrical figure, with a funnel-shaped 

 depression at each end. It consists of concentric rings, 

 which are supposed by some to increase in number with 

 the age of the animal. The vertebne are destitute of 

 articular processes, and when in union, form through- 

 out the whole column cavities composed of two cones, 

 joined at the base. These cones contain a cartilaginous 

 substance formed of concentric fibres, of which those 

 next the centre are the softest. By mean* of this car. 



tilage the vertebrae are united, and upon it they per- 

 form all their movements. In the cartilaginous fishes 

 all the vertebrae are consolidated together, so that the 

 spinous processes can only be distinguished. 



The vertebrae may be divided into the cervical, dor- 

 sal, and caudal. In osseous fishes, the cervical vertebra; 

 are in general wanting, although in some cases they ex- 

 ist, as in the herring, to the number of four. In the 

 cartilaginous kinds, they are ossified into one piece. 

 The dorsal vertebra are easily recognised, by wanting 

 processes on the interior part. These have generally 

 on the sides transverse processes, to which the ribs are 

 attached. The coudal '^erleirce are possessed of spinous 

 processes, both on the superior and interior surfaces. 

 In those fish which are flat these are very long, as in 

 the flounders. The first caudal vertebra is in general 

 of a peculiar shape. The cavity of the trunk is termi- 

 nated by its inferior process. In the flounders it is 

 large, round in the fore part, and terminated below by 

 a sort of spine. The last caudal vertebra is however 

 more remarkable than the first. It is almost always of 

 a triangular form, flat, and placed vertically. Upon its 

 posterior extremity it bears articular impressions, which 

 correspond to the small and delicate bones of the fin of 

 the tail 



The number of the bones of the vertebral column in 

 different speaies being exceedingly various, suggested 

 to Artedi the use of this character in the separation of 

 nearly allied species Among the species of the genus 

 t ;, prinus, for example, a difference in the number of 

 \i rtflmi 1 has been observed to the amount of fourteen. 

 In ascertaining this character, Artedi recommends the 

 greatest circumspection. The fish should be boiled, the 

 fleshy parts separated, and the vertebrae detached from 

 one another, and these counted two or three times in 

 succession to prevent mistakes. This character is of 

 great use, as it is not liable to variation, individuals of 

 the same species exhibiting the same number of verte- 

 bra; in all the stages of their growth. 



The number and size of the rifitare likewise extreme- 

 ly various. The cartilaginous fishes may be considered 

 as destitute of true ribs. Where they exist, as in the 

 osseous fishes, they are articulated to the body of the 

 vertebra, or to the spinous processes. They are forked 

 in some fishes, and in others double ; that is, two ribs 

 proceed from each side of every vertebra. In the genus 

 Cyprinus they are of a compressed shape; in the cod 

 they are round ; and in the herring like bristles. 



The number of the ribs likewise furnishes a charac- 

 ter in the discrimination of species, which may be safe- 

 ly relied on in the absence of more obvious characters. 



Besides these bones which we have enumerated, there 

 are many more osseous spicula?, which serve to support 

 the fins, and to strengthen the muscles. Indeed the ex- 

 istence of numerous bones, unconnected with the skele- 

 ton, is a distinguishing character of the osteology of 

 fishes, and these we shall afterwards consider in our 

 account of the different purposes to which they are sub- 

 servient 



The composition of the bones of fishes has never been 

 investigated with sufficient care. It is well known, that 

 they never acquire so great a degree of hardness and 

 rigidity as the bones of the mammalia or birds : hence 

 we may safely conclude from the facts connected with 

 the process of ossification in other animals, that the bones 

 of fishes abound in gelatinous and cartilaginous matter, 

 while the portion of earthy or saline matter is small. 

 The earthy salts are phoephute and carbonate of lime, 

 and the phosphate of magnesia, the former predomina- 



