206 PISCES. 



bones. The superficial layer of the external side arises from the 

 clavicle, and covers entirely that which lies beneath it ; that also of 

 the inner surface of the fin, or the one turned toward the trunk, 

 exhibits similar relations. The latter draws the fin toward the body, 

 while the external, as abductors of the fin, move and raise it out- 

 ward. 



The arrangement of the muscles upon the posterior extremities, or 

 ventral fins, when the latter are present, is of a similar kind. Here 

 we find proper elevators and depressors in a double series, which 

 arise from the pelvis and are inserted into the fin-rays. The rudi- 

 mentary pelvic bones obtain fasciculi from the lateral muscles, that 

 correspond to an oblique abdominal muscle and a rectus. 



The muscles of the anterior extremities, or pectoral fins, are par- 

 ticularly developed in Lophius and in the Flying Fish, e. g. Trigla, 

 Exocaetus, among the Osseous Fishes. 



The muscles of manducation are very strongly developed, and form 

 more or less a mass constituting what is called the cheek-flesh of 

 Fishes, and which in the Trout has a particularly delicate taste. 

 The whole depression occupying the external surface of the articular 

 portion of the temporal bone is covered by this muscular mass ; and 

 it arises not only thence, but also from the anterior edge of the 

 praBOperculum, and is inserted partly into the upper, partly into the 

 lower jaw. The disposition of these manducatory muscles is very 

 different from that of the masseter and temporal muscles of the higher 

 animals, to which, however, they correspond. 



The muscles of the Cartilaginous Fishes exhibit more noticeable 

 diversities. In the Plagiostomi, as the Rays, the dorsal and ventral 

 muscles are more separated by a horizontal tendinous layer, that 

 divides each lateral muscle into an upper and lower half. Several 

 muscles are also given off for the cranium, so that the head can be 

 slightly moved. Remarkably large horizontally expanded layers form, 

 in the Rays, the muscles for the great pectoral fins, without, however, 

 these admitting of a separation into superficial and deep layers, as in 

 the Osseous Fishes. In the Electric Ray a pair of peculiar muscles 

 with long tendons also occur ; their fleshy part or bellies arise behind 

 the skull from its lower surface, and are inserted into the anterior 

 margin of the head in front of the electric organs ; they have no analogue 

 in other Fishes. 



In the Cyclostomi the same numerous tendinous strips are found 

 intersecting the lateral muscles, which are here much developed, 

 and surround the body. In the Myxinoides we find superadded a 



