28 BULLETIN OF THE BUREAU OF FISHERIES. 



literature, however, thus far no previous reference to or description of this differentia- 

 tion of the great lateral muscle in other fishes has been found other than the sentence 

 of Miescher's quoted below." Miescher speaks of "a thin muscle plate lying along the 

 side of the body just beneath the skin which degenerates strikingly (cutaneous muscle)." 

 I interpret this statement as referring to the lateralis superficialis, though there is 

 nothing else in the context that suggests that Miescher recognized this portion of the 

 lateral muscle as a differentiation out of the total mass. The differentiation is described 

 in part by the papers of the senior author dealing with subjects in salmon anatomy and 

 physiology.* 



Histologically the superficialis is distinguished from the profundus by its strikingly 

 different type of muscle fibers. The fibers of the superficialis are more compact, more 

 unifonn in diameter, and relatively smaller in size than the fibers of the profundus. 

 The fat-storing property of this muscle has been specifically described in a previous 

 paper.*^ Analyses made of this muscle showing the percentage of fat in the fish from 

 the mouth of the Columbia River gave the total of the fat in the fresh wet muscle as 

 high as 30 per cent. In no other muscle of the salmon is such an enormous quantity 

 of fat stored, and especially nowhere else are such quantities stored within the fibers. 



MUSCULUS LATERALIS PROFUNDUS. 



This muscle forms the major portion of the great lateral muscle as defined above. 

 It extends from the occiput and pectoral girdle to the base of the caudal fin. The 

 muscle is characterized in the fish of first quality especially by its rich pink color. The 

 body of the profundus fills the entire space between the superficialis and skin on the 

 one hand, and the skeletal complex on the other. The two divisions, the epaxial and 

 the hypaxial, are very sharp and distinct for the entire extent of the muscle. The 

 attachments of the muscle are better understood after a discussion of the arrangement 

 of its segments. 



The profundus is distinguished from the superficialis always by its characteristic 

 difference in color, as previously referred to. The king salmon in the Columbia River 

 shows an especially rich color in this muscle, though the color fades as the period of 

 starvation progresses during the spawning migration. The form and size of the fibers 

 vary within wide limits while the length of the individual fibers remains more 

 constant. In contradistinction to the superficialis the fibers of the profundus vary 

 in diameter from 25 or 30 to as much as 200 or 250 micra. No such variation in size 

 occurs in the fibers of the superficialis. This characteristic alone is sufficient to diag- 

 nose the two muscles. 



a Miescher, Friedrich: Statistische und biologische Beitrage zur Kenntniss vom Leben des Rheinlachses im Siisswasser. 

 Schweizerischer Fischerei-Ausstellung zu Berlin, 1880, p. 186. Also reprinted in Histochemische u. Physiologische Arbeiten 

 von Friederich Miescher, 1S97, p. 145. Miescher's e.xact -words are: "Am slarksten degenerirt eine gesonderte diinne Muskel- 

 platte, die an der Seite des Korpers direct unter der Haut liegt (Hautmuskel)." 



& Greene, Chas. W.: The storage of fat in the muscular tissue of the king salmon and its resorption during the fast of the 

 spawning migration. Bulletin U. S. Bureau of Fisheries, vol. xxxiil, 1913. 



c Greene, Chas. W-; A new type of fat storing muscle in the salmon, Oncorhynchus tschawytscha. American Journal of 

 Anatomy, vol. 13, 1912, p. 175-17S. 



