SKELETAL MUSCULATURE OF THE KING SALMON. 4I 



with the third. The insertion of the fourth is into the extreme ventral portion of the 

 cartilage of the fourth ceratobranchial. 



Fifth division. — The fifth division is regarded as a subdivision of the preceding 

 muscle. It has its origin in a tendinous raphe which is strongl}' developed at a point 

 ventral to the insertion of the preceding. Some fibers also arise from the cartilaginous 

 plate posterior to the insertion of the fourth division. The muscle is relatively short 

 and thick. It is attached by a short, stout tendon to the fifth ceratobranchial, its 

 tendon being fused with the anterior border of the tendon of the pharyngo-clavicularis 

 extemus. 



TR.\NSVERSI VENTRALIS, ANTERIOR. 



A short thick triangular bundle of fibers arises on the median surface of the ventral 

 end of the ceratobranchial of the fourth arch. It is an unpaired muscle and runs directly 

 across to an attachment at the corresponding point on the opposite side. 



TRANSVERSI VENTRALIS, POSTERIOR. 



This stout unpaired muscle is very much like the preceding, but three times larger. 

 It runs from the inner surface of the base of the fifth ceratobranchial transversely under 

 the esophagus to a corresponding insertion on the opposite ceratobranchial. 



The transversi ventrales by their contractions approximate the ventral portions 

 of the fourth and fifth arches of the branchial basket. 



PHARYNGO-CLAVICULARIS EXTERNUS. 



This is a short broad muscle band extending from the antero-dorsal surface of the 

 clavicle directly dorsalward to the lower surface of the fifth ceratobranchial. Its length 

 is only about three times its breadth. Its contractions depress the branchial arch. 



PHARYNGO-CLAVICULARIS INTERNUS. 



This is a broad thin muscle band arising from the anterior surface of the inner 

 margin of the clavicle at about the middle of its arch. Its fibers run diagonally forward 

 and inward to an insertion on the ventral margin of the fifth ceratobranchial just under 

 the insertion of the pharyngo-clavicularis extemus. There is a strong tendinous line 

 along the upper margin of the muscle. 



The intemus muscle retracts the branchial basket, i. e., draws it backward toward 

 the esophagus. 



MANDIBULAR AND HYOID ARCH MUSCLES. 



INTERMANDIBULARIS. 



A short thick unpaired muscle extends transversely from the left dentary to the 

 right. In cross section it is a rough oval 17 by 6 mm. The muscle is 2 cm. long. It is 

 attached to the inner surfaces of the two dentaries just back of the symphysis. It serves 

 to approximate the mandibles. 



GENIOHYOIDEUS. 



This is a broad flat sheet of muscle arising from the ceratohyal. The origin is 

 along a diagonal line extending from the postero-ventral border to the antero-dorsal 

 margin of the bone. The muscle joins with its fellow to form a practically continuous 



