152 MUSCULAR SYSTEM. 



directed obliquely downwards and backwards, the second 

 (b } ) downwards and forwards, the third (c 9 ) like the first, and 

 the fourth (?,) like the second. The upper series of lateral 

 muscles (#,) attached anteriorly to the occipital bone, occupy 

 the deep cavity on each side of its projecting spine, and 

 extend backwards to the longitudinal diverging tendons and 

 muscles of the caudal fin, in which they terminate. The 

 oblique direction of all these lateral muscles increases the 

 velocity of their motions, as in the intercostals of quadru- 

 peds. These strata of muscles are arched backwards, having 

 all their convex surfaces directed forwards, and as their fibres 

 pass obliquely backwards and peripherad, they draw their 

 cutaneous attachments forwards and inwards when the ver- 

 tebrae are the fixed points. They are attached also to the 

 temporal bone and to the back part of the scapular arch, and 

 the inferior series (d,) extends forwards under the arms (n,) 

 to the os hyoides. The layers of these large lateral muscles 

 of the trunk are seen similarly disposed in the cylindrical 

 body of the cyclostome fishes, in the compressed trunk of 

 most of the osseous forms, and also in the broad depressed 

 body of the flat fishes. They correspond with the vertebrae 

 into which their aponeuroses are inserted, and they are at 

 once analogous to the muscles of the segments of articulata 

 and to the more lengthened and isolated muscles of the ver- 

 tebral column and trunk in higher vertebrated classes. The 

 flat surfaces of the interspinous bones (/,) are covered with 

 diverging muscular fibres, which pass downwards and move 

 them in every direction, and exterior to these are larger dis- 

 tinct muscular fasciculi which are inserted into the broad 

 bases of the rays of the median fins, for their varied move- 

 ments. The longitudinal straight muscles which extend 

 along the median line of the dorsal and the abdominal sur- 

 face of the trunk are interrupted by the dorsal and anal fins. 

 The longitudinal straight muscle of the back in fishes generally 

 commences from each side of the spine of the occipital bone, 

 and proceeds in two separate fasciculi to be inserted into the 

 base of the anterior ray of the first dorsal fin. When there 

 are more than one dorsal fin, it is extended in two fasciculi 

 from the last ray of each of these fins to the first ray of the 

 next, and it is continued in the same manner (#,) from the 

 last dorsal to the beginning of the caudal fin. On the ven- 



