MUSCULAR SYSTEM. 153 



tral surface of the body, the first pair of straight muscles 

 generally pass from the scapular arch or the humeri to the 

 anterior part of the pelvis, the second pair (e,) commence 

 from the pelvis, and passing on each side of the anus, con- 

 tinue to the first ray of the anal fin (h.) They are developed 

 between the anal fins, as between the dorsal, when there are 

 more than one, and from the last ray of the posterior anal 

 fin they are continued backwards to the beginning of the 

 caudal fin. By these longitudinal straight muscles above 

 and below, the median fins are moved and supported, and 

 the trunk is moved in a vertical plane. The sides of the 

 head are occupied by two large and powerful muscles, (&, /,) 

 apparently analogous to the masseter and the temporal 

 muscles, and which pass forwards and downwards to be in- 

 serted into the lower jaw. The lower jaw is depressed both 

 by muscles passing backwards from it to the os hyoides, and 

 by those which extend from the os hyoides to the scapular 

 arch. The operculum is raised by two or more short and broad 

 muscles, placed at its upper part, and is depressed by short 

 round muscles placed on the inner surface of the same part. 

 The branchiostegal rays are moved by short oblique muscles, 

 which descend from the opercular bones to these rays, and 

 by others which are interposed obliquely between each pair 

 of rays, like intercostal muscles in higher classes. The 

 branchial arches, in the osseous fishes, are attached by dis- 

 tinct muscles to the back part of the skull, to the sides of 

 the vertebrae, and also to the scapular arch and the os 

 hyoides. In the cartilaginous fishes, where there is no oper- 

 culum over the branchiae, that apparatus is covered exter- 

 nally with a layer of short muscles, like intercostals, passing 

 between soft cartilaginous bands, like ribs. The pectoral 

 fins, or arms, have on each of their flat surfaces a band of 

 adductor and abductor muscles, (Fig. 71-/>) which extend 

 from the scapular arch to the commencement of the pha- 

 langes or rays. These muscles act also as flexors and exten- 

 sors of the arms, and correspond with the magnitude of these 

 organs ; they are greatest in the expanded pectoral fins of 

 the plagiostome fishes. The ventral fins or feet are also 

 moved by two similar muscles (Fig. 71- ^ 5 ) on each of their 

 flat surfaces, extending from the pelvic bones to the com- 

 mencement of the rays, and corresponding in size and 

 strength with the magnitude of the feet. The anguillifo rm 



