Nos. IAND2.] ANATOMY OF SCOMBER SCOMBER. m 



bones that cover the cheek of the fish. Posterior to the middle 

 part of the postorbital part of the infraorbital series these scale- 

 like bones are firmly bound to each other and to the infraorbital 

 bones by fibrous tissue, and so form a sort of bony armor cover- 

 ing the cheek. Posterior to the dorsal and ventral parts of the 

 postorbital series they are less firmly connected with each other 

 and look like ordinary scales, although they are much larger and 

 stouter than the scales on the trunk of the fish. Posteriorly these 

 scales or scale-like bones extend backward beyond the anterior 

 edge of the preoperculum onto the outer surface of the operculum, 

 becoming gradually smaller and more delicate. 



The orbital edges of the infraorbital bones all turn inward. Im- 

 mediately distal to this turned-in portion they are all traversed by 

 the circumorbital part of the main infraorbital lateral canal. One of 

 the bones of the series, usually the second or fourth from the 

 dorso-posterior end of the chain, does not usually reach the edge 

 of the orbit, being excluded from it by the adjoining edges of 

 the two bones between which it lies. 



The dorso-posterior bone of the series is somewhat larger and 

 stouter than the bones that immediately adjoin it, and seems, un- 

 questionably, the homologue of the postfrontal bone of Aniia. It 

 lies partly superficial to the anterior end of the dilatator operculi 

 muscle; and partly superficial to the dorsal end of the levator 

 arcus palatini. Its dorsal edge lies superficial to the lateral edge 

 of the dilatator groove, and is nearly parallel to, but separated by 

 a considerable space from, the dorsal edge of the ridge of bone 

 that separates the dilatator groove from the temporal groove. 

 The antero-dorsal corner of the bone reaches almost to the ante- 

 rior end of the dilatator groove ; and the orbital edge of the bone, 

 which is presented ventro-anteriorly, rests upon the orbital edges 

 of the frontal bone and the postorbital ossification. 



Ventral to the postfrontal bone, between it and the lachrymal, 

 lie the postorbital and suborbital bones of the fish. The four or 

 five most dorsal ones are relatively slender bones, often with 

 pointed posterior ends. The next bone, the sixth or seventh from 

 the dorsal end of the series, is, after the lachrymal, the largest 

 bone of the series. It lies directly behind the eye and has an 

 irregularly rounded hind edge, which, in large fishes, extends 



