318 PROCEEDINGS OF THE CANADIAN INSTITUTE. 
3. AppuctoR Hyomanpisutaris, (No. 26, Cuv. in part ; Depressor 
suspensiori, Stan.; Depressor opercul, Ow., in part.) 
This muscle is very closely related to the add. operewl, 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. 
Innervation.—Ramus opercularis facials. 
Action.—It aids the add. are. pal. 
The relations of this muscle correspond almost exactly with those 
of the corresponding muscle in Perea. In Hsox, 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. 
IIIl.—OPERCULAR MUSCLES. 
1. Levaror Opercutt, (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 facralrs. 
Action.—It pulls the operculum upwards and slightly forwards, 
helping the dilatator. 
2. Ditatator Opercutt, (No. 25, Cuv., anterior part ; Lev. operculi, 
ant. part, Ow.) (Fig. 2, Dil. Op.) 
This muscle lies immediately below and behind the /ev. are. 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- 
