SKELETAL MUSCULATURE OF THE KING SALMON. 27 



II. Supracarinales, the dorsal longitudinal muscles. 



3. Protractor dorsalis. 



4. Retractor dorsalis. 



III. Infracarinales, the ventral longitudinal muscles. 



5. Protractor ischii. 



6. Retractor ischii (protractor analis). 



7. Retractor analis. 



DIVISIONS OF THE GREAT LATERAL MUSCLE. 



The great lateral muscle, as the term is applied to the adult fish, does not include 

 the dorsal and ventral differentiations given in II and III of the above list. It does, 

 however, include all the muscle mass extending from the base of the skull and the pec- 

 toral girdle to the base of the caudal fin except the supracarinales and the infracarinales, 

 respectively. This mass, as just described, is divided longitudinally into four actual 

 divisions. An epaxial and a hypaxial portion is formed by the lateral line septum. 

 Each of these great divisions is differentiated longitudinally into a thin superficial por- 

 tion and a thick deeper portion as previously indicated. Each of these may now be 

 described in fuller detail. 



MUSCULUS LATER.'^LIS SUPERFICIALIS. 



This muscle extends over the surface of the deeper division of the great lateral 

 muscle, the profundus, for its full extent from the head to the base of the tail. It is 

 thickest in the mid-lateral line. There are two separate and distinct portions, the 

 epaxial and hypaxial divisions. Each of these divisions forms a thin sheet, becoming 

 thinner as it extends out from the lateral line, dorsally in the epaxial and ventrally in 

 the hypaxial divisions, respectively. The muscle is several millimeters thick in the 

 king salmon in the lateral line region, while its extreme dorsal and ventral borders are 

 represented in thickness by only a few fibers. The dorsal Umit of the superficialis is 

 along the line about two-thirds the distance from the lateral line to the mid-dorsal 

 line of the salmon body. The ventral division varies somewhat in its extent. In the 

 anterior portion of the body the superficialis extends only about one-half the distance 

 from the lateral line to the mid-ventral line. In the posterior part of the body the mar- 

 gin of the superficialis extends two-thirds to three-fourths this distance. These epaxial 

 and hypaxial divisions of the superficialis muscle are sharply separated from each other 

 by the lateral line septum. 



The muscle as a whole is characterized by a darker appearance than the profundus. 

 The latter is the usual salmon pink color in the well-conditioned fish, though lighter in 

 color in the fish of poorer quality. The superficialis is separated from the profundus by 

 a rather weakly marked sheet of connective tissue. In macerated examples the super- 

 ficialis can readily be separated from the profundus. On the whole, however, the two 

 muscles are very intimately connected. Histologically the demarcation line is sharp 

 and distinct, but by methods of gross anatomy this line is not so readily determined. 



The superficialis has been observed by the senior author in a number of other 

 fishes. In some of these, for example the California sardine, Clupanodon cceruleus, 

 this muscle is relatively more highly developed than in the king salmon. In the 



