A NEW TYPE OF FAT STORING MUSCLE IN 



THE SALMON, ONCORHYNCHUS 



TSCHAWYTSCHA 1 



CHAS. W. GREENE 



Department of Physiology and Pharmacology, Laboratory of Physiology. 

 University of Missouri 



TWO FIGURES (ONE PLATE) 



The king salmon, Oncorynchus tschawytscha, like a number of 

 other fishes, possesses a thin and superficial muscle lying along 

 the side of the body just under the lateral line. This muscle 

 extends the full length of the body of the fish from the pectoral 

 girdle to the caudal peduncle. 2 It is thickest at the lateral line 

 and becomes gradually thinner as it spreads out in a sheath over 

 both the dorsal and the ventral surfaces of the deep portion of the 

 great lateral muscle. In transverse section the shape of the 

 muscle on each side is that of two scythes placed together base 

 to base. When the muscle tissue is coagulated, as in heating, its 

 dark appearance makes it stand out with prominence. In so far 

 as the king salmon is concerned this dark muscle presents charac- 

 teristics of peculiar interest which seem to me to justify a special 

 characterization and report. 



The dark muscle is a differentiated portion of the lateral muscle 

 mass. Its fibers run in a longitudinal direction. The muscle is 

 broken into short segments, myomeres, by transverse connective 

 tissue bands, the myocommata. In comparison with the remain- 

 der of the great lateral muscle, the profundus, the dark muscle is 

 characterized by its relatively small fibers. These fibers are very 

 compactly arranged having a minimum of interstitial connective 



1 Published by permission of the I*. S. ( !ommissioner of Fisheries. 



2 In an anatomical description of the salmon muscles I have given this muscle 

 the name, 'musculus superficialis lateralis.' The deep portion of the great lateral 

 muscle is called the 'musculus profundus lateralis.' Paper now in manuscript. 



175 



THE AMERICAN JOURNAL OF ANATOMY, VOL. 13, NO. 2 



