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ALUS. [Vol. XVIII. 



backward, the layer becoming gradually thinner in its upper and 

 posterior portions, and finally disappearing as a distinct fibrous 

 structure. In this fascia-like layer the scales of the cheek, and the 

 delicate scale-like postorbital bones, have their insertions. It is, 

 therefore, a special formation of the corium. Its principal in- 

 sertion is on the internal surfaces of the lachrymal and suborbital 

 bones. When it, and the bones to which it is attached are re- 

 moved, the adductor mandibulse, levator arcus palatini and dila- 

 tator operculi, are exposed. The levator maxillse superioris, as a 

 separate muscle, is not found in Scomber, but it is represented, 

 apparently, by certain tendons found associating with different 

 parts of the adductor mandibulse. 



The Adductor Mandibul^ (Figs. 54 and 55) presents three 

 well-defined portions ; a superficial portion, A.^, a deeper portion, 

 A^A^, and a mandibular portion, A^» 



A-^, the superficial portion of the adductor, arises almost entirely 

 from the upper portion of the outer surface of the preoperculum, 

 a few fibers only, at the extreme upper corner of the muscle, aris- 

 ing from the outer surface of the hyomandibular. The fibers 

 of the muscle run downward and forward, crossing, externally, 

 the lower half of the levator arcus palatini and the upper half of 

 AoAo. At its lower end the muscle separates slightly into two 

 portions, the division not extending far into the muscle and ap- 

 parently not having any special morphological significance. Those 

 fibers of the muscle that arise from the hyomandibular form a 

 small and somewhat separate bundle on the inner surface of the 

 muscle. The outer surface of the muscle is marked by several 

 faint, tendinous lines, not shown in the figures, and on its inner 

 surface, along its antero-dorsal edge, there is a long, tendinous 

 band which gives insertion, at about the middle of its length, to 

 a tendinous formation which doubtless represents, in part, one 

 of the divisions of the levator maxillse superioris. 



Along the middle portion of the inner surface of the distal half 

 of the muscle, there is a broad longitudinal tendinous band, from 

 which, at the distal end of the muscle, two tendons arise, an 

 anterior and superficial one, and a posterior and deeper one. The 

 fibers of the muscle are all inserted in this tendinous band, none 



