MUSCULAR SYSTEM OF FISHES. 



379 



diately underneath the integuments are shown in 

 Fig. 194, where m, m, are the great lateral muscles, 



producing the flexion of the body and tail : d is the 

 dorsal fin, which is raised by the muscle d ; p, the 

 pectoral fin, expanded by the muscle p: v, the 

 ventral fin, moved by the muscles situated at v : a, 

 the anal fin, in like manner moved by muscles at 

 its base a : and c, the caudal fin, the muscles for 

 moving which are seen at c .• o is the operculum, or 

 flap, which covers the gills ; and n, the nasal cavi- 

 ties, or organs of smell. The form of the body, and 

 disposition of the skeleton, allow of their being- 

 inserted immediately on the parts which they are 

 intended to approximate. Hence the use of long 

 tendinous cords is dispensed with.* 



The actions of the muscles are easily understood 

 from the nature of their insertions. In general, the 

 direction of the fibres is in some degree oblique, 

 with reference to the motion performed. Two 

 series of muscles are provided for the movements 

 of the tail, which consist almost exclusively of 

 lateral flexion, the whole spine in some degree par- 

 ticipating in this motion. These muscles occupy 



* Between tlie layers of flesh, however, there occur slender semi- 

 transparent tendons, which give attachment to a series of short 

 muscular fibres, passing nearly at right angles between the surfaces 

 of the adjoining plates. See Sir Anthony Carlisle's account of this 

 structure in the Philosophical Transactions for 1806. 



