STORAGE OF FAT IN MUSCULAR TISSUE OF KING SALMON. 79 



amount of interstitial connective tissue; and (4) most important of all, by its enormous 

 loading of fat. 



Muscidus lateralis profundus, the lateral pink muscle. — The profundus, or the deep divi- 

 sion of the great lateral muscle, is the pink salmon muscle as it is ordinarily spoken of. 

 It has a totally different appearance from the superficial dark muscle. The fibers of 

 the pink muscle vary enormously in size, from 40 up to 250 /t in diameter in the adult. 

 The average size of the fibers varies somewhat in different regions of the pink muscle 

 even of an adult fish. In the young salmon, 10 to 15 cm. long, there is a greater range 

 of variation than in the adult, as is shown by the outline figure 16, plate x. This 

 is due to the fact that the fibers are undergoing longitudinal cleavage which is very 

 unequal. This cleavage leads to a large number of very slender fibers. It is the method 

 of reproduction of new fibers which leads to the irregular outlines noted in the cross 

 sections of all the fibers of the profundus of the salmon, both young and adult. 



The amount of supporting connective tissue in the pink muscle is relatively great. 

 Beside the blood vessels, a large amount of adipose tissue is present. It is the adipose 

 tissue of the pink muscle, which is heavily loaded with fat, that carries the greater 

 part of the fat of the salmon commercial products. 



Myocommata of the great lateral muscles. — The myocommata which separate the 

 muscle myomeres are always crowded with fat in the normal adult salmon. These con- 

 nective tissue partitions are composed of white fibrous connective tissue into which the 

 short longitudinally placed muscle fibers are attached. The tissue is largely filled with 

 adipose cells. Its fat cells are large and relatively uniform in size when filled. They 

 form a considerable mass within the myocommata most thickly studded near its center. 

 There are also large numbers of fat cells on the surface and crowded beneath the ends 

 of the muscle fibers. This fat forms no inconsiderable portion of the storage fat present 

 in the adult salmon. 



Supracarinales. — There are longitudinal-paired muscles along the middle of the 

 back of the salmon. These extend from the head to the dorsal fin, the supracarinales, 

 and from the dorsal fin to the adipose fin and to the dorsal lobe of the caudal fin. These 

 paired muscles are cylindrical in shape and about the size of a lead pencil in the thickest 

 part, but spreading out somewhat anteriorly. The muscles are of interest in this con- 

 nection chiefly because they are imbedded in a relatively thick and prominent mass 

 of adipose tissue. In a prime fish this adipose tissue is crowded with fat. 



Infracarinales. — A similar collection of adipose tissue is even more striking along 

 the mid-line of the belly of the salmon. The fat of the belly surrounds the protractor 

 ischii anteriorly and the retractors posteriorly. The mass is from i to 2 cm. thick and 

 twice as wide in a prime 80 cm. fish. The cylindrical muscles inclosed will be about 

 0.8 to 1.5 cm. in diameter, and the rest of the area an almost solid mass of fat cells. 

 In a fish low in fat the fat is taken up, leaving a white fibrous connective tissue mass. 

 These two areas of adipose tissue form a considerable storehouse of salmon fat. 



Muscles of the fins. — The storage of fats in the fin muscles has been studied only 

 sufficiently to demonstrate the type. Adequate comparisons have not been made to 

 make the observations complete, except in establishing the normal type. The fin muscles 

 of the pectoral, ventral, dorsal, anal, and caudal fins (the deep caudal muscles) are much 

 alike in general fat loading. Sections of the erectors and of the depressors of the anal 

 fin have been most extensively examined. The two muscles are much alike in general 



