FISH IN GENERAL. GO 



of the branchial apparatus ; 2d, there is often another depres- 

 sor further back ; 3d, the levator of the same arch rising behind 

 the orbit, and inserted towards the summit of the temporal, is 

 the opponent of the former, and widens the palatine arcade 

 and the branchial space. Thus by the action of two articula- 

 tions, the movement of respiration is kept up in the animal 

 while life lasts. 



The muscles of the operculum produce a movement similar 

 to that of the palatine arches ; they are placed behind it, one 

 external is the levator, adhering to the external crest of the 

 mastoidean, and serves to raise the gill ; and the other inter- 

 nal, the compressor to close it, is fixed to the lateral inferior 

 surface, where the great ala and petrous bone join it to the 

 mastoidean. It is separated from the depressor of the palatine 

 arch by the bundle of superior anterior muscles of the bran- 

 chiae. The sub-opercular and interopercular bones have no 

 particular muscles ; they move with the operculum, and with 

 the palato-temporal arch ; and the muscles which approximate 

 the branches of the hyoid, and contract the branchiostegous 

 membrane, assist also in bringing the palatine and opercular 

 structures nearer together. 



The principal muscle of the hyoid bone corresponds to the 

 genio-hyoidean ; it comes from the internal surface of the 

 branch of the inferior jaw near the symphysis, is carried over 

 the hyoidean branch, and inserted upon the first of its two 

 great pieces. The two genio-hyoideans are often united by 

 the transverse fibres ; chiefly of their middle part. Moreover, 

 the muscles placed between the branchiostegous rays likewise 

 draw the branches together of the hyoid, and a part of the 

 great lateral acts as a sterno-hyoidean. A layer of fibres lies 

 usually along the internal face of the branchiostegous rays ; 

 some arise from the inside of the operculum, and pass over 

 the rays, adhering by cellulosity, and forming a kind of 

 purse round each branchial cavity. A pair of muscles 



