316 FISHES. 



The deep seated are concealed to a great extent between the two 

 large muscles of the body ; they adhere to the interspinous small 

 bone, two before (No. 3), and two behind (No. 4), the one being 

 separated from the other by the crests of this small bone, and inserted 

 at the base of the ray, which they can elevate or depress behind, or 

 even carry from the side when the anterior and posterior of the same 

 side act in unison ; but the latter description of motion is invariably 

 but slightly marked. 



Muscles of the Shoulder. 



The girdle which forms the shoulder of fishes, and Avhich is com- 

 posed of the bones called by us supra-scapular, scapular, and 

 humeral, is susceptible of merely a very circumscribed faculty of 

 motion ; and, indeed, it may be regarded rather as a fixed point for 

 those of the trunk, the branchiae, and inferior jaw. Nevertheless, if 

 we suppose that these other parts should be themselves fixed for an 

 instant, then this girdle may be drawn backwards by the great lateral 

 muscles of the body (No. 1), of which it receives a considerable 

 portion. 



It is justifiable, likewise, to represent the shoulder as deriving 

 motion forwards, from the part of this same muscle (d, c), which 

 goes to the body of the os hyoides, where a fixed point for it to 

 act upon is given, when this bone is brought nearer to the jaw by 

 the genio-hyoidean muscle, and when the jaw itself is closed by the 

 crotaphites. 



There is in some species a muscle, which, on the posterior, infe- 

 rior, and lateral side of the cranium, is carried to the superior and 

 anterior part of the humeral bone, and which partly invests the 

 membrane that performs the office of a diaphragm between the 

 cavity of the branchiae and that of the body. It must act on the 

 shoulder but very feebly, and its destiny more probably is to act on 

 the diaphragm and to compress the intestines. In the perch it does 

 not extend (No. 10), except from behind the mastoidean to the supra- 

 scapular and scapular. 



The coracoid stylet has not what may be exactly called a peculiar 

 muscle, but, as before mentioned, it is encased in the great lateral 

 muscle of the body. Sometimes, it merely gives attachment to a thin 

 and oblique muscular layer, which partially covers this great muscle. 



Muscles of the Pectoral Fin. 



In the large number of species where the carpal bones are small, 

 these muscles are only inserted in the rays. 



On each surface there are two layers all of which terminate by as 

 many long tendinous slips as there are rays. The direction of the 

 two layers on each surface is a little crosswise. The anterior super- 

 ficial layer (No. 14) comes from the humeral bone and descends, 

 whilst the deep seated layer (No. 15) arises from the external sur- 

 face and the inferior edge of the ulnar bone ; it ascends. This 

 arrangement is the inverse of that of the posterior layers, for in the 

 latter the layer nearest the bones descends, whilst the other ascends. 

 When the two layers of the anterior surface act in unison, they 



