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THE OSTEOLOGY OF AMIURUS CATUS. 291 
subcutaneous system, and the latter to the system of the branchios- 
tegal rays. Hollard' sums up his observations thus, “ En d’autres 
termes et pour nous résumer, il résulte pour nous de cette étude que 
le battant operculaire des Poissons se divise, quant 4 sa signification 
anatomique, entre le squelette normal et un squelette supplémentaire 
et cutané ; que l’interopercule appartient au premier, comme naissant 
et se développant dans le premier arc viscéral ; qu’il occupe la méme 
place que l’enclume des mammiféres ; qu’entin l’opercule et le sous- 
opercule, loin de lui faire suite, loin de pouvoir étre assimilés aux 
autres osselets de l’ouie ou a vrais appendices, sortent des limites du 
névro-squelette, non, comme le voulait Cuvier, 4 titre de piéces sans 
analogues mais en se rattachant au développement si général et si 
considérable des expansions tégumentaires des Poissons.” Owen? 
does not commit himself definitely either way, considering them 
merely appendages to the ‘“ tympano-mandibular arch,” but however 
implies a certain amount of credence in the auditory theory, by 
referring them to the mandibular rather than to the hyoid arcade. 
Lastly, Gegenbaur® suggests that the interoperculum was originally 
a part, not of the hyoid skeleton, but of the mandibular. 
It is now a recognized fact that the homologues of the auditory os- 
sicles are not to be looked for in the opercular bones, and we have 
remaining the theories that they are a subcutaneous system, a part of 
the branchiostegal system, and that the interoperculum is a part of 
the mandibular arcade. In Anuwurus they seem to belong to the 
branchiostegal system, with the exception of the preoperculum. This 
is formed round a mucous canal, and is one of what may be called 
the mucous canal series, to which also the infraorbital ossicles belong. 
Functionally it is not one of the opercular bones but protects the in- 
cluded mucous canal. The suboperculum is properly a bone lying 
below the lower edge of the operculum. This is the position it holds 
Esox, also in Salmo, but in the latter case it is increased in size, and 
‘projects largely from under the operculum. In both these forms 
also it hes on the inner side of the interoperculum. In Anuwrus, 
what is usually considered the upper branchiostegal ray bears exactly 
the same relations. Shortly behind its attachment to the epihyal, 
1 Hollard.- De la signification de l’appareil operculairedes Poissons. Ann. des Sci. Nat.» 
1864. 
2 Owen.—On the anatomy of the vertebrates. Vol. I., London, 1866. 
3 Loc. vit. 
