Nos. IAND2.] ANATOMY OF SCOMBER SCOMBER. 197 



thirds its length. This tendon has a nearly rectangular surface, 

 and gives origin, on both sides, to the fibers of the muscle. The 

 anterior edge of the tendon coincides with the anterior edge of 

 the muscle, and at its origin the tendon is as wide as the muscle. 

 At its distal end it is only about two thirds as wide as the muscle. 

 The distal half of the muscle is crossed, nearly at right angles, 



The Dilatator Operculi (Do) occupies the entire dilatator 

 groove, arising, in that groove, from the dorsal surface of the 

 frontal, postorbital ossification and squamosal. The dorsal fibers 

 of the muscle run backward and downward; the ventral fibers 

 almost directly backward. Nearly all of them are inserted on a 

 longitudinal tendon, the outer edge of which is seen as a tendinous 

 line on the outer surface of the muscle. This tendon begins not 

 far from the extreme anterior end of the *muscle, and, running 

 downward and backward, is inserted on the operculum on the 

 flat, projecting edge of bone that forms the superficial or antero- 

 lateral edge of the facet by which the operculum articulates with 

 the hyomandibular. The deep edge of the tendon, in its anterior 

 part, has its origin on the ridge that separates the dilatator groove 

 into its antero-lateral and postero-mesial portions. A few of the 

 fibers of the muscle are inserted, with its tendon, directly on the 

 operculum. The muscle crosses externally the posterior, squamosal 

 head of the hyomandibular; crosses externally a small, dorso- 

 posterior corner of the levator arcus palatini ; and passes partly 

 internal to the projecting dorsal end of the preoperculum. It 

 lies mesial to the foramen by which the ramus oticus facialis 

 reaches the dorsal surface of the skull, and those branches of that 

 nerve that supply organs 11 and 12 in the squamosal run upward 

 and mesially along the external surface of the muscle and then 

 pass inward between the muscle and the lateral surface of the 

 ridge of bone that separates the dilatator and temporal grooves. 

 The muscle must accordingly, in acquiring its origin on the dorsal 

 surface of the skull, have crowded in between the nerve and the 

 canal it innervates, either pushing the nerve laterally or the canal 

 mesially. 



The Intermandibularis (Ini, Fig. 57) is a small, much de- 

 generated muscle, lying between the rami of the mandibles and 



