THE MYOLOGY OF AMIURUS CATUS. 319 
low the first portion of lev. arc. pal. The tendon passes obliquely 
backwards and is inserted into the anterior and upper surfaces of the 
process by which the operculum articulates with the hyomandibular. 
The origin of the muscle is continued backwards on the ventral sur- 
faces of the frontal and sphenotic, a few fibres arising from the lat- 
ter behind the postorbital process, and posteriorly a few take origin 
from the surface of the hyomandibular and from the ridge on its 
posterior superior angle. The majority of these fibres unite with the 
strong tendon, only those which arise from the hyomandibular being 
inserted directly into the opercular knob. 
Innervation.—It is innervated by a branch of the nerve which 
supplies the superficial portion of add. mand., 7. e., a branch from the 
trigeminus arising behind the branch for the deep portion of add. 
mand. and add. tent. 
Action.—Raises the operculum, and swings it outwards on its ar- 
ticulation with the hyomandibular. 
In £sox this muscle is weak and does not extend forwards beyond 
the posterior extremity of the articulation of the hyomandibular 
with the pterotic. In Perca it reaches the sphenotic, but in none 
does it extend as far as in Amiwrus. In other Teleosts the innerva- 
tion is from twigs from the branch of A. maw. inf. trigemini, which 
supplies the lev. arc. pal., while here the innervation would indicate 
a closer relationship with the add. mand. 
3. AppDuCTOR OperRcuLI, (No. 26, Cuv.; Depressor operculi, Stan. et 
Ow.) . 
This may be seen by cutting through the insertion of the levator 
operculi and reflecting it, or better, by the dissection required for 
exposing the add. arc. pal. and add. hyomand. It arises from the 
inferior surface of the pterotic, and is inserted into the posterior edge 
of the upper border and the upper part of the inner surface of the 
operculum. 
Innervation.—Ramus opercularrs facralis. 
Action.—Approximates the operculum to the side of head, and is 
therefore the opponent of lev. and dil. operculi. 
