Nos. IAND2.] ANATOMY OF SCOMBER SCOMBER. 229 



one of the two deeper ones, are usually more or less continuous, 

 and are undoubtedly parts of a single muscle in process of 

 separation. 



The superficial muscle {Adds, Figs. 50, 51), which naturally 

 lies mesial to the other two, is a broad, flat rectangular muscle. 

 It arises from the anterior edge of the dorsal part of the mesial 

 surface of the clavicle, the surface of origin beginning near the 

 dorsal end of the antero-dorsal process of the bone, and extending 

 downward somewhat below the level of the central point of the 

 scapulare. Its fibers run almost directly backward, and, becom- 

 ing tendinous near their distal ends, separate into separate tendons 

 each of which is inserted on the eminence found on the mesial 

 half-bone of each of the dermal rays immediately distal to its 

 proximal end. None of the tendons of the muscle are usually 

 inserted on either of the first five most dorsal rays of the fin. 

 The action of this muscle is, as shown by its origin and insertion, 

 to pull the fin mesially and downward against the trunk. It is 

 the adductor superficialis of ]\Icj\Iurrich's descriptions. 



The two deeper mesial muscles (Addp) are also adductor 

 muscles. The more dorsal one of the two is a triangular muscle, 

 the surface of origin of which lies, in its ventral two thirds, im- 

 mediately internal to and anterior to that of the superficial mus- 

 cle. Dorsal to the latter muscle the surface of origin of the 

 deeper muscle extends upward and forward along the dorsal edge 

 of the postero-dorsal process of the clavicle, for about one half 

 its length. The muscle, as already stated above, is usually some- 

 what continuous with the superficial muscle. Its fibers converge 

 strongly, and, separating into several bundles, are inserted by 

 tendons on those rays that lie between the propterygial ray and 

 the most dorsal one of those rays that give insertion to the tendons 

 of the superficial muscle; the insertions being, like those of the 

 latter muscle, on the eminence found on the mesial half-bone of 

 each of the rays concerned. No part of this muscle is inserted 

 on the propterygial ray. The muscle thus pulls the dorsal edge 

 of the fin mesially without acting directly upon its ventral portions. 



The ventral one of the deeper muscles is a flat muscle larger 

 than either of the other two. It has a large surface of origin, 

 arising from the mesial surface of the ventral half of the scap- 



