PHILOSOPHY OF ZOOLOGY. 



they are placed about the mouth, or on the upper part of 

 the head. They are in general soft, but often contain one 

 jointed ray. They do not differ in structure from the fins, 

 and are so closely connected with them, that it is difficult 

 to point out their use. It is not probable that they are 

 organs of touch, as many have imagined, but rather peculiar 

 modifications of fins. 



The muscles which move the fins, and all the other or- 

 gans of the body, are of a paler colour than in the animals 

 of a higher order. They are also more uniform in their 

 substance, being in general destitute of tendinous fibres. 

 In the greater number of fishes, there are no muscles pecu- 

 liar to the head. The sides are furnished with the most 

 powerful ones, to execute the lateral movements of the 

 animal. These muscles are disposed in layers or arches, 

 with the convexity towards the head. The different mus- 

 cles are strengthened by small detached spines, imbedded 

 among the fibres of the muscle, and giving them additional 

 strength. Between the layers there is in general a quantity 

 of viscid albuminous matter interposed. After death, this 

 fluid speedily'undergoes a change, and can seldom be observ- 

 ed in fishes which have been kept a few days. But in recent 

 fish, when boiled, the albumen appears coagulated in the 

 form of white curd, between the layers of the lateral muscles. 

 The motions of fish are performed by means of its fins. 

 The caudal fin is the principal organ of progressive motion. 

 By means of its various flexures and extensions, it strikes 

 the water in different directions, but all having a tendency 

 to push the fish forward ; the action resembling, in its man- 

 ner and effects, the well known operation of the sailor 

 termed skulling. The ventral and pectoral fins assist the 

 fish in correcting the errors of its progressive motions, and 

 in maintaining the body steady in its position. BORELLI 

 cut off, with a pair of scissars, both the pectoral and ventral 



