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Show 182 ON 'l'HE THUO'I'UHE OF 'I'HE SKULL. The hyoidean arch con i ts of two median bones,-an anterior, the. "entoglossal," whi h supports the tongue; and a posterior, the "urohyal." Its lat ral cornua arc forn1ed by four bones, two snutll (basi-hya0, and two large (epi and cerato-hyals) on each ·ide, th latter supporting the "branchiostegal rays" on which the bran hio t gal 1nembrane is spread out; and the upper of th two larg r bones is connected with the synchondrosi between the byomandibnlar and symplectic by a styliform bone-th stylo-hyal (Fig. 71, Ry.). Thus, the hyo1nandibular may be r ganl d as mnmon to the mandibular and the hyoidean arche , supporting the former, indirectly, by means of the ympl ctic, and th latter directly, by means of the stylo-hyaL The stylo-hyal very probably corr spond with the styloid process and pyramid of 1\ian, but it i diffi nlt to find any very sure footing for our int -rpr tations b yond thi point. The manner in which th ympl cti is connected, on the one hand, with the repr sentative of the incus, and, on the other hand, with that of the tyloicl pro e._ and pyramid, is strongly suggestive of a relation b twe n thi bono and the stapes. But it must no less be admitted that similar argum nt. might Le used in favour of the stap lial haracter of the hyomandibular bon , the articulation of which with the pro-oti and opisthotic might be compared with the fitting in f the stn,pes into the fenestra ovalis, which i bound d by th e two bones; or again, plausible argu1nents 1night be brought forwn,rd in favour of the view that the hyomandibnlar, at any rat , i a bone special to fishes. At present, it n1ay b well n1cr ly to indicate these various possibilities, iV the study of develo1)lnent has hardly been carried sufficiently far to enn,Lle u to cl cide in favour of one rather than of another. Each of the four anterior branchial arches is composed of four bones, and the branchial arch s of pposite sides are united by connecting cartilages and median ossifications. The anterior or first arch, which corresponds with the greater cornu of the hyoid of Man, is fixed to the pro-otic bone, between the exits of the trigeminal and the po'J'tio dut·a, by cartilage. rrhe succeeding arches have no osseou.· or cartilaginous representatives in Man. THE S1'HUOTUTIE OF 'I'HE PIKE'S SKULL. 183 The branchiostegal rays attached to the epi-hyal and cerato-hyal are in like case. Three bones, the operculurm ( Op.), sub-operculum (8. 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-operculUJn is connected by ligament with the angular piece of the jaw, the sub-operculum lies between the two. The gill-cover is developed from the outer surface of tho 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 homologues of these bones in Man. The pre-operculum, which, as I have stated above, binds together the l1yomandibula.r 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 representativeB of the ossicula auditus are certainly not altogether unfavourable to this view. These are the most important bones in the Pilre's skull, but several yet remain for consideration. Thus there is a sn1all, 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 connected with, or attached close to, the post-frontal. Finally, in the Pike, a forked bone, the supra-scapula, suspends 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 hy the exa1nination of the bones of the skull pro1Jer. There is a certain identity of fundamental plan upon which |
