SKELETAL MUSCULATURE OF THE KING SALMON. 53 



ADDUCTOR VENTRALIS SUPERFICIALIS. 



This muscle represents the most dorsal portion of the pelvic musculature. The 

 muscle is separated into two divisions, as described by Harrison for Salnio salar. 



The pars anterior arises from the dorsal surface of the anterior end of the ischium and 

 along the line of aponurosis in which the median longitudinal septum, the abdominal 

 peritoneum, and the ventral attachments of the great lateral muscles meet. The pars 

 anterior division of the muscle runs as a flat band to end in a broad tendinous sheet 

 which covers the dorsal surface of the caudal end of the profundus just over the posterior 

 end of the ischium. It is inserted into the dorsal half rays of the external six or seven 

 rays. The insertion is into the cun'ed bases of the rays at about the middle of the 

 curve. 



The pars posterior consists of the short and relatively thick mass of muscle fibers 

 which arise from the fascias along the lower border of the lateral muscle immediately 

 dorsal to the posterior part of the ischium and the insertion of the fin. These fibers 

 are well separated from the pars anterior. The fibers run abruptly downward and 

 posteriorly to an insertion into the bases of the last three or four anal rays, i. e., the rays 

 on the median border of the fin. The tendinous insertion does not seem to be sharply 

 subdivided into slips and is extremely short. 



ADDUCTOR VENTRALIS PROFUNDUS. 



The profundus arises from the dorsal surface of the illium for its full extent, and from 

 the horizontal septum extending from the inner margin of the illium to the mid-ventral 

 line, also from a similar septum extending from the external margin to the skin. The 

 fibers constitute the largest muscle of the pelvic series. In the middle of the belly the 

 muscle is broad and rather thick (22 mm. broad by 6 mm. thick, in an 80 cm. fish). 

 Posteriorly the muscle is somewhat heavier on its median border, the fibers extending 

 transversely out and back over the posterior thickened margin of the illium, and under 

 the tips of the dorsal half rays. When the adductor superficialis is removed the ten- 

 don of the profundus is revealed as a broad and relatively long sheath. The insertions 

 of the tendon are on the inner, that is median, borders of all the dorsal half rays. This 

 tendon enters also into the formation of the capsule of the movable joint by which the 

 fin is attached to the posterior end of the illium. 



Contractions of the adductor profundus lead to two motions, first, rotation of the 

 fin over the illium at this point, i. e., throwing the fin up against the body of the fish, 

 and second, the spreading of the rays, by throwing the outer fin margin in a lateral 

 direction with reference to the median plane of the fish. These last motions, it will be 

 seen, are directly the opposite of those produced by the abductor group. 



The ventral margin of the lateral muscle is strongly attached into the supporting 

 connective tissue of the posterior part of the illium by means of the myocommata. It 

 is evident that contractions of the lower borders of the myomeres lying immediately 

 posterior to the pelvic girdle will have a tendency to draw the pelvic arch as a whole 

 backward. The muscular development does not seem to be of an extent which would 

 lead one to infer that this is a chief function of the muscle. It justifies only the infer- 

 ence that the movement is an incidental but possible one. 



