318 PROCEEDINGS OF THE CANADIAN INSTITUTE. 



3. Adductor Hyomandibularis, (No. 26, Cuv. in part ; Depressor 

 suspensiorii, Stan.-; Depressor operculi, Ow., in part.) 



This muscle is very closely related to the add. operculi, lying im- 

 mediately in front of it and partly overlapped by it. It arises from 

 the lower surface of the pterotic, and passes downwards, outwards 

 and forwards, to be inserted into the hyomandibular immediately 

 above the opercular process. 



Innervate on. — Ramus opercularis facialis. 



Action. — It aids the add. arc. pal. 



The relations of this muscle correspond almost exactly with those 

 of the corresponding muscle in Perca. In Esox, however, it is merely 

 a part of the add. arc. pal., while in the Cyprinoids it has a much 

 greater origin and insertion than in any of the other forms. 



Ill— OPERCULAR MUSCLES. 



1. Levator Operculi, (No. 25, Cuv.) (Figs. 1 & 2, LOp.) 



The levator of the operculum is exposed by removing the integu- 

 ment from the side of the head and stripping off the posterior 

 continuation of the fascia covering the add. mand. This poste- 

 rior continuation is not directly continuous with the anterior 

 portion, but takes origin from the posterior edge of hyomandibular 

 and preoperculum, and is attached above to the edge of the pterotic 

 and below to the upper surface of the operculum, being posteriorly 

 continuous with the fascia covering the trunk musculature. The 

 muscle arises from the posterior edge of the ridge on the hyomandi- 

 bular, and from the edge of the pterotic. Its fibres are directed 

 downwards and slightly backwards, and are inserted into the whole 

 upper border of the operculum. 



Innervation. — R. opercularis facialis. 



Action. — It pulls the operculum upwards and slightly forwards, 

 helping the dilatator. 



2. Dilatator Operculi, (No. 25, Cuv., anterior part ; Lev. operculi, 



ant. part, Ow.) (Fig. 2, Dil. Op.) 



This muscle lies immediately below and behind the lev. arc. pal., 



and is closely related to it. The anterior part forms a very 



strong tendon, which arises by muscular fibres from the under 



surface of the frontal and ectethmoid above the orbit and be- 



