SKELETAL MUSCULATURE OF THE KING SALMON. 



57 



The longer muscle slips of the inclinator are about 1 2 to 15 mm. long and from 4 to 5 

 mm. wide. They are broad at their origin and the fibers converge to the point of insertion 



into the rays. 



The origin of the inclinator fascicuU is from the skin and the fascia covering the 

 ventral border of the great lateral muscle. This broad origin gives to each slip a base 

 which is seated on the cylindrical border of the lateral muscle. From this broad origin 

 the fibers converge toward a short slender tendon which is inserted into the base of the 

 corresponding ray on its lateral surface, and between the tendons of the erector and 

 depressor respectively. The insertion is in the plane of the axis 

 of the ray joint. The incUnator muscle slips fill the triangular 

 space between the skin, the lateral muscle border, and the 

 erector-depressor group of muscles (see fig. 13). The divisions 

 are strongly embedded in connective tissue sheaths as best 

 shown in formalin-preserv^ed specimens. 



Contractions of the inclinator muscle strongly bend the fin 

 toward the corresponding side. This motion is most pro- 

 nounced at the anterior margin of the fin where the muscle 

 slips are longer and larger. The pull of the muscle is at an 

 angle of about 70°, an angle that decreases with the flexion of 

 the fin in that direction. 



ERECTOR-DEPRESSOR MUSCLE COMPLEX. 



When the great lateral muscles are removed from the region 

 of the anal fin a muscular mass is exposed lying under the 

 superficial and deep lateral muscles and covering the interhema 

 spines of the anal fin. This mass consists of alternate slips of 

 muscles constituting the erector and depressor muscles of the 

 anal fin respectively. 



The whole group of muscle divisions is, Hke that of the 

 dorsal fin, covered with a fibrous connective tissue sheath of 

 considerable thickness. This sheath is continuous with that 

 between the interhemal spines and is especially well developed in the longitudinal line 

 marking the border between the hemal spines and the interhemals. 



Fig. 12. — Section across the anal 

 fin in the plane of the interhe- 

 mal spines, the fin rays, and 

 the erector-depressor group of 

 muscles; int., interhemal 

 spine; d. a., depressor analis; 

 inc., inclinator anaUs muscle; 

 a. r., anal ray. 



ERECTOR ANALIS. 



The erector muscle of the anal fin is composed of the larger of the alternate divisions 

 mentioned above as constituting the deep muscle complex. There is a muscle sHp for 

 each fin ray. 



Each erector slip arises from the posterior margin of the interhemal spine in front 

 of the one to which the ray is attached, and from the entire surface of the connective 

 tissue septum between the two interhemals in question. Each muscle division is spindle 

 shaped. It tapers at its ventral end into a short tendon, which runs to an attachment 

 in the anterior basal margin of the corresponding fin ray. 



