170 LECTURE VII. 



tab. iv.) : a full and accurate detail of the myology of the Myxinoids, 

 together with a philosophical comparison of the muscular system of 

 Fishes generally with that of the higher Vertebrata, will be found 

 in XXI. pp. 179-246. But the determination of the special, serial, 

 and general homologies, and the recognition of the various individual 

 adaptive modifications, of the muscles of Fishes, still remain a rich 

 and little-explored field for the labours of the myologist. 



The normal character of Ichthyic myology shows itself in the vast 

 proportion of the vegetatively repeated myocommata, corresponding 

 with the vertebral arches, as compared Avith the superadded system 

 of muscles subservient to the action of their diverging appendages : 

 but this condition, which, inasmuch as it deviates so little from the 

 fundamental type, throws so much light upon the essential nature 

 and homologies of the muscles of the Vertebrata, is not less ad- 

 mirably and expressly adapted to the habits and medium of existence 

 of the Fish. The interlocked myocommata of the trunk constitute, 

 physiologically, two great lateral muscular masses, adapted by their 

 attachments, and especially by those of the anterior and posterior 

 ends, to bend vigorously from side to side, with the whole force of 

 their alternating antagonistic contractions, the caudal moiety of the 

 trunk ; producing that double lash of the tail by which the fish darts 

 forwards with such velocity. When the lateral muscles are more 

 violently contracted, so as to bend the whole trunk, the recoil may 

 even raise and propel the fish some distance from its native element : 

 thus the salmon overleaps the roaring cataract which opposes its 

 migration to the shallow sources whither an irresistible instinct 

 impels it to the business of spawning ; and thus the flying-fish, in the 

 extremity of danger, bafiles its pursuer by springing aloft, and pro- 

 longs its oblique course through the air by the rapid fiuttering of its 

 outspread pectorals. When the anterior portions of the great lateral 

 masses act from the trunk as a fixed point upon the head, they move 

 it rapidly and forcibly from side to side : in this way the Siluri deal 

 severe blows with their outstretched serrated pectoral spines ; thus 

 the Percoid and Cottoid Fishes strike with their opercular spines ; 

 and so likewise may the Saw -fish (Pristis), and Sword-fish {Xiphias), 

 wield their formidable weapons, although their deadly cut or thrust is 

 commonly delivered with the whole impetus of the onward course, 

 the head being rigidly fixed upon the trunk. 



The supra-carinales, combining with the dorsal portions of the 

 myocommata, give tension to the region of the back, slightly raise 

 the tail, and depress the dorsal fins. The infra-carinales, in combi- 



