78 BULLETIN OF THE BUREAU OF FISHERIES. 



The splendid keeping qualities of many of the scarlet-red preparations made during 

 the investigation is attributed to a thorough neutralization of the alkali in the bath 

 of acid water. 



TYPES OF SALMON MUSCULAR TISSUE AS REGARDS THE STORAGE OF FAT. 



The musculature of the salmon " is relatively simple. The main mass consists of 

 the great lateral muscle of Cuvier. A number of smaller muscles are associated with 

 the various fins and with the structures in the head region. But the storage of fat takes 

 place chiefly in the great lateral muscles. 



Great trunk muscles. — The great lateral muscles include the major masses of muscu- 

 lar tissue along the sides of the body from the head and the pectoral girdle to the base 

 of the tail. These masses represent from 60 to 70 per cent of the total weight of the 

 mature fish when in prime condition. 



The great lateral muscle of the salmon has lately been described.* In Amiurus'^ it 

 is described as divided into five longitudinal portions more or less distinct. In the salmon 

 there is a connective tissue septum, the lateral line septum, running the length of the 

 body just under the lateral line. It separates the lateral muscle into a dorsal and a 

 ventral portion, each of approximately the same size. Aside from this there is no further 

 subdivision along the lines designated by McMurrich. 



However, the great lateral muscle is divided into two distinct muscles on the basis 

 of the well-marked anatomical and histological differentiations that have taken place. 

 There is a superficial thinner portion which is anatomically distinct and easily identi- 

 fiable because it is darker in color; and a deeper, wider, and thicker mass which is pink 

 in color. These two divisions are well separated by a thin lamina of fibrous connective 

 tissue bearing an excess of adipose tissue in most of its extent. The lateral line septum 

 separates both the superficial and the deep muscles into dorsal and ventral divisions. 



The fin muscles, and to a less extent the head muscles, are the ones in the most 

 constant but slight activity in the daily life of the fish, and, strangely enough, whether 

 for this reason or not, these muscles are not largely loaded with reserve fat. 



Musculus lateralis super ficialis , or dark lateral muscle. — The superficial dark muscle 

 forms a type of tissue with respect to its loading of fat that has not previous to the 

 preliminary notices of the present writer "^ been described, in so far as I can discover, 

 though it was noted by Miescher.' He undoubtedly refers to the superficial lateral 

 muscle when he says: "A thin muscle plate lying along the side of the body just be- 

 neath the skin degenerates most strikingly (Hautmuskel)." Miescher makes the refer- 

 ence quoted'' in the brief discussion of the microscopic picture of the fat in the so-called 

 fatty degeneration. 



This muscle is characterized by the following points: (i) Its compact arrangement 

 of fibers; (2) the smallness and uniformity of size of the fibers; (3) the relatively small 



^ It does not seem wise to regard the supracarinales and iniracarinales as divisions of the lateral muscle in the ordinary sense 

 of the designation. 



^Greene, C. W. and Carl H.: The skeletal musculature of the king salmon. Bulletin U. S. Bureau of Fisheries, vol. 

 xxxm. 1913 (1914), p. 21-60, pi. i-ii. 



c McMurrich, J. P.: The myology of Amiurus catus. Proceedings of Canadian Institute, n. s., vol. n, 1884, p. 328. 



^Greene. Charles W.; A new type of fat-storing muscle in the salmon, Oncorhynchus tschawytscha. The American 

 Journal of Anatomy, vol. xni, p. 175, 1912. Also an undescribed longitudinal differentiation of the great lateral muscle of 

 the king salmon. Anatomical Record, vol. vii, p. 99, 1913. 



< Miescher, op. cit., p. 186 (145). 



