SKELETAL MUSCULATURE OP THE KING SALMON. 



37 



The cephalic portion of the muscle in the medium sized fish is about 4 cm. broad in the 

 anterior posterior extent and about 5.5 cm. in the dorso-ventral dimension. The thick- 

 ness is from i to 1.5 cm. 



(6) Mandibular portion of the adductor. — Besides the cephalic portion of the adductor 

 there is a stout mandibular portion. It arises from the anterior border of the tendon 

 over the quadrate bone and the angle of the mouth. It extends anteriorly to an attach- 

 ment along the inner surface of the middle third of the dentary, i. e., from a point directly 

 below the angle of the mouth forward to a point on the jaw. At the origin of this 

 portion the fibers are continuous with the fibers of the cephalic portion. From the 

 origin the fibers diverge slightly as they are distributed to their attachments on the 

 dentary. The lower margin of the muscle takes a continuous attachment along the 

 under and inner surface of the 

 bone. The upper and outer 

 side of the muscle remains free 

 from attachments. 



The contraction of the 

 adductor closes the mouth 

 with great power. In addi- 

 tion to its function in feeding 

 it undoubtedly takes part in 

 the motions of respiration. 



LEVATOR ARCUS PALATINI. 



This is a short, thick, 

 comparatively wide muscle 

 which takes its origin from the 

 angle formed in the external 

 surface of the sphenotic, filling 

 the space just posterior to the 

 eyeball. The fibers run ob- 

 liquely downward and backward to a broad insertion on the anterior surface of the 

 superior half of the hyomandibular and also into the superior margin of the metaptery- 

 goid. The muscle at its posterior dorsal margin is intimately associated with and often 

 inseparable from the fibers at the origin of the dilatator operculi muscle. 



DILATATOR OPERCULI. 



Fig. 3. — Superficial head muscles after removal of the skin and a part of the jaws. 

 >l. C, adductor mandibulae, cephalic portion; A. m., Adductor mandibuliE, 

 mandibular portion; L. P., levator arcus palatini; Z>. op., dilator operculi; 

 L, of?., levator operculi; P. d., protractor dorsalis; Lat.. lateral muscle. 



This muscle has its origin from the anterior margin of the external surface of the 

 pterotic and the posterior border of the sphenotic. Its fibers converge sharply backward 

 and downward to an insertion by a small but strong tendon into the upper margin of 

 the opercle. The attachment is on the knob formed at the junction of the opercle with 

 the hyomandibular. The muscle lies in the groove between the exposed margin of the 

 pterotic and the hyomandibular. 



