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., i.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 Esox 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 Amiurus. In other Teleosts the innerva- 

 tion is from twigs from the branch of R. max. inf. trigemini, which 

 supplies the lev. arc. pal. t while here the innervation would indicate 

 a closer relationship with the add. mand. 



3. Adductor Operculi, (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. 



1 1 enervation. — Ramus opercularis facialis. 



Action. — Approximates the operculum to the side of head, and is 

 therefore the opponent of lev. and dil. opercnli. 



