• 48 



to each ray. These muscles take their origin from the fibrous tissue whicli covers the 

 lateral muscles and which is continuous with the fibrous layer of the skin. Each 

 rnuscle is inserted into the side of a fin-ray outside its articulation, but the end of 

 the muscle also has connections by means of fibrous tissue with the ends of the 

 interspinous bones. 



The elevators and depressors lie beneath the abductors : there is one elevator and one 

 depressor on each side of the body to each fin-ray. In the greater part of the fins the 

 heads of the interspinous bones are between the bases of the fin-rays, and each 

 elevator lies along the posterior half of the side of an interspinous bone, while each 

 depressor lies along the anterior half These muscles are considerably smaller than 

 the abductors. They are inserted into the bases of the fin-rays in front and behind and 

 take their origins from the surface of the interspinous bones and intermediate fibrous 

 membrane. Their inner ends extend beneath the outer edges of the lateral muscles, 

 which are free. The elevators and depressors of the fin-raj^s are shown in Plate XII. 

 along the whole of the ventral side of the body and the anterior part of the dorsal 

 side, while the abductors are shown along the posterior three-fourths of the dorsal side. 



The muscles of the rays of the pectoral and pelvic fins are closely similar and require 

 no special description. 



The muscles of the ventral region of the head may be classified according to their 

 functions into two divisions — the masticatory and the respiratory, the former moving 

 the jaws, the latter the branchial arches. 



The most powerful of the masticatory muscles is the common jaw muscle, which 

 partly corresponds to the temporal and masseter muscles in man. Its origin occupies 

 the outer surface of the " suspensorium," i.e., the system of bones to which the 

 mandible is articulated, and part of the surface of the skull. It consists of two portions, 

 a superficial and a deeper, the former arises from the hyomandibular and the anterior 

 edge of the preoperculum, and from the anterior part of the sphenotic, and from the 

 basal portion of the right frontal ; the deeper portion is smaller and arises from the 

 metapterygoid, symplectic, and quadrate. Between the two portions runs a large nerve, 

 the mandibular branch of the fifth cranial nerve. Both portions of the muscle on the 

 right side of the head terminate in a tendinous structure which divides into two 

 tendons, the upper is longer and thinner and is inserted into the middle of the posterior 

 edge of the maxilla, the lower is shorter and broader and is inserted into the upper edge 

 of the mandible, chiefly into the articular bone, a little in front of the articulation of 

 the mandible with the quadrate. It is evident that the chief function of this muscle is to 

 bring the jaws together, which it does principally by powerfully pulling the mandible 

 upwards, while its upper tendon draws the upper jaw downwards and backwards. The 

 muscle on the left side of the head is somewhat larger than on the right, and is inserted 

 only into the mandible, the tendon passing to the maxilla Ijeing entirely absent. 



The levator suspensorii is a muscle which arises from the sphenotic, especially from 

 the lateral process of that bone, and is inserted into the head of the hyomandibular. 



