THE STRUCTURE OF THE PIKE'S SKULL. 183 



The branchiostegal rays attached to the epi-hyal and cerato-hyal 

 are in like case. 



Three bones, the operculum {Op.), sub-opereulum (S.Op.), and 

 inter-operculum (I.Op.\ are developed within the membranous 

 gill-cover, and serve to strengthen it (Fig. 65). The operculum 

 is articulated with the posterior and inferior process of the 

 hyomandibular bone ; the inter-operculum is connected by liga- 

 ment with the angular piece of the jaw, the sub-operculum lies 

 between the two. 



The gill-cover is developed from the outer surface of the 

 second visceral arch, and corresponds with the concha of the 

 ear in the human subject ; and as the latter part contains no 

 osseous elements, it is obviously in vain to seek for the homo- 

 logues of these bones in Man. 



The pre-operculum, which, as I have stated above, binds 

 together the hyomandibular and the quadrate bone externally, 

 has been compared with the tympanic bone of Man, and the 

 position of the bone and its relations to the representatives 

 of the ossicula auditus are certainly not altogether unfavourable 

 to this view. 



These are the most important bones in the Pike's skull, but 

 several yet remain for consideration. 



Thus there is a small, oval, supra-orbital ossicle (S.Or., 

 Fig. 65) attached to the outer margin of the frontal, above the 

 orbit, and an inverted arch of sub-orbital bones which bound the 

 orbital cavity externally and inferiorly. The sub-orbital series 

 consists of a large anterior bone, which lies beside the nasal, and 

 of five or six smaller bones, the hindermost of which is con- 

 nected with, or attached close to, the post-frontal. 



Finally, in the Pike, a forked bone, the supra-seapula, sus- 

 pends the scapular arch to the apices of the squamosal and 

 epiotic bones. This bone, it need hardly be said, is without a 

 distinct osseous representative in Man. 



The merely anatomical comparison of the facial bones of the 

 Pike with those of Man thus leads to a conclusion very similar to 

 that attained by the examination of the bones of the skull proper. 

 There is a certain identity of fundamental plan upon which 



