204 



ALUS. [Vol. XVIII. 



ridge, the notch, the degenerate muscle fibers stretching across 

 the notch, and the insertion of the adductor opercuU along the 

 ridge, all seem to indicate that this is a region where two branch- 

 iostegal rays have fused. 



The adductor operculi, both at its origin and at its insertion, is 

 directly contiguous with the adductor hyomandibularis. Its fibers, 

 however, have a different direction from, and are entirely separate 

 from, those of that muscle. 



The Levator Operculi {Lo, Figs. 54 and 55) arises im- 

 mediately above the dorso-posterior end of the posterior articular 

 head of the hyomandibularis, from the thickened hind end and 

 edge of the dorsal ridge of the squamosal. Its fibers run down- 

 ward and backward, radiating from the small surface of origin, 

 and are inserted in the depressed region on the dorsal portion of 

 the inner surface of the operculum. It lies immediately ex- 

 ternal to the adductor operculi, but its fibers cross those of that 

 muscle at a considerable angle. At its origin it is immediately 

 contiguous with the dilatator operculi, and its anterior fibers are 

 parallel to, and in immediate contact with, the posterior fibers of 

 that muscle. 



3. Muscles Innervated by the Nervus Glossopharyngeus and 



Nerviis Vagus. 



The Levatores Arcuum Branchialium (Figs. 59 and 60) 

 are, as in Amia, seven in number, two interni and five externi. 

 The muscles do not however, in Scomber, all arise together, as 

 they do in Amia, and there is, in Scomber, a ligament connecting 

 the first arch with the skull, not found, or not found equally de- 

 veloped, in Amia. 



The two^interni (Labi", Labi'') arise, with the externi of the 

 third and fourth arches {Labe. III. -IV.), from the lateral surface 

 of the skull, in a horizontal line that extends the full length of 

 the intercalar and slightly overlaps anteriorly the squamosal and 

 petrosal. The surface of origin (Fig. ii) is wider posteriorly 

 than anteriorly, and lies along, and immediately below, the sharp 

 ridge that extends forward across the intercalar from the hind 

 end of its suprascapular process. Anteriorly the surface of 

 origin crosses the ventral corner of the squamosal, and extends 



