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4. ADDUCTOR MANDIBULAE AND LEVATOR ARCUS PALATINI 



MUSCLES. 



The adductor mandibulae is completely separated into dorsal and mandibular portions. The 

 dorsal portion is a large muscle, almost completely separated into two divisions, a superficial and a 

 deeper one. The superficial division is apparently the homologue of the muscle A t of Vetter's de- 

 scriptions of other teleosts, the deeper division representing the two muscles A, and A 3 of the same 

 descriptions. The mandibular portion of the muscle is the muscle A 0J of Vetter's nomenclature, and 

 lies wholly in the mandible. The mandibular branch of the nervus trigeminus, in its course to enter 

 the mandible, passes between the muscles A t and A 2 A 3 . 



The muscle A x arises from the outer edge of the preopercular, there lying, in its dorsal portion, 

 directly external to the levator arcus palatini, and in its ventral portion directly external to a portion 

 of A, A 3 . The fibers of the dorsal two-fifths, approximately, of the muscle do not reach the pre- 

 opercular, being inserted on a broad thin tendinous band which crosses the outer surface of the 

 levator and has its insertion on the preopercular. The fibers of the muscle all run forward in a nearly 

 parallel course, and are inserted on a tendinous band that extends the füll length of the anterior 

 «dge of the muscle. The dorsal end of this band becomes a short stout tendon which has its insertion 

 on the mesial surface of the shank of the maxillary, the ventral end of the band joining the tendon 

 of the muscle A 2 A 3 . The anterior edge of the tendinous band gives attachment to the fibrous tissues 

 that line the lateral surface of the mucous membrane that extends from the ventral edge of the palato- 

 quadrate to the internal surface of the maxillary, and it is in this fibrous tissue that the maxillo- 

 mandibular ligament, already described, has its course, lying close along the anterior edge of the 

 muscle A v This maxillo-mandibular ligament must accordingly be acted on by the muscle A 1; and 

 hence serves in part as its tendon of insertion; a contraction of the ventral fibers of Aj rotating the 

 maxillary. In Scomber the tendon of A 1 is inserted on the internal surface of the lachrymal, the 

 maxillo-mandibular ligament in part giving insertion to the deeper portion, A 3 , of the adductor 

 (Allis, '03, p. 192). 



The muscle A 2 A 3 is much thicker and stouter than A l5 and has its origin on the external 

 surface of the body of the metapterygoid, near its hind edge, and, ventral to the metapterygoid, on 

 the anterior surface of the preopercular. The muscle is incompletely separated into dorso-internal 

 and ventro-external portions which may represent A 3 and A» respectively, the fibers of A 3 all pass- 

 ing internal to the external bündle of the levator arcus palatini, while the fibers of A 2 pass external 

 to or lie wholly ventral to that muscle. The fibers of both portions of the muscle at first converge 

 slightly forward, and then contract rapidly, and are all, or nearly all inserted on a large tendon 

 which passes into the mandible. The few fibers that are sometimes not so inserted form a broad, thin 

 superficial sheet, the fibers of which separate from the deeper fibers of the muscle and have their 

 insertion in a tendinous formation on the inner surface of the muscle A v The large tendon A 2 A 3 

 separates into three parts. The middle one of these three parts arises mainly in relation to the 

 fibers of A 3 , the other two arising mainly in relation to the fibers of A 2 and A x these two tendons 

 lying the one postero-ventral and the other antero-dorsal to the middle tendon. The middle tendon 

 runs downward and forward, and has its insertion on the mesial surface of the articular immediately 

 dorsal to the hind end of Meckel's cartilage. The postero-ventral tendon runs forward and downward 

 across the lateral surface of the middle tendon, and then turns rather sharply downward, passes 



