MUSCULAR SYSTEM OF FISHES. 



167 



its proper muscles, which rise from the sustaining hyoidean arch. 

 A more constant and important muscle rises from the operculum and 

 suboperculum, and attaches itself to the inner surface of the branchi- 

 ostegal rays, expanding over the whole membrane of the bi-anchial 

 chamber, and the more completely as the chamber becomes more 

 circumscribed, and its outlet smaller. In the Lepidosiren the homo- 

 logous muscle rises not only from the suboperculum but from the 

 ramus of the jaw, and, meeting its fellow along a median raphe 

 beneath the head and hyoid arch, represents the 'mylo-hyoideus'* 

 The muscular investment of the branchial chamber of the Torpedo 



(45. r) receives a fasciculus 

 -i^ from the scapula, and sends 

 another {ib. o) forwards to the 

 cranium, from which the con- 

 strictor of the electric battery 

 is continued. 



In most osseous fishes there 

 is a decussating pair of 

 muscles (depressores branchi- 

 ostegorum) which rise from 

 the base of one ceratohyal, 

 and are inserted into the lower 

 branchiostegals of the oppo- 

 site side. 



The levator and abductor 

 muscle (44, s) of the pectoral 

 fin rises from the coracoid, 

 and descends obliquely to its 

 insertion by distinct fasciculi 

 into the bases of the fin -rays : 

 the depressor and abductor {t) 

 of the pectoral is deeper seated, and usually rises from the radius ; 

 it ascends to its insertion. There are two posterior or adductor 

 muscles, whose fibres are oblique and decussate, but in opposite di- 

 rections to the abductors, and tending also, in separate action, to 

 raise or depress the fin. There are small special muscles in most 

 fishes for divaricating the fin rays. The muscles of the pectoral fin 

 are well developed in sharks ; enormously so in the skate and 

 torpedo, where the horizontal position of the fin involves further 

 modifications. In^fig. 45. the letter s shows the ' levator pectoralis,' 

 and t the upper radiated muscle of the digits. 



Muscles and Electric Batteriesof the Torpedo. Carus- 



XXXIII. p. 358. pi. 24. fig. 4. a. 

 M 4 



