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Show 002 ON 'l'HE STRUCTURE OF THE VERTEBRATE SKULIJ. of the structure of the completely ossified brain-case is, I belieYe, the best that has yet been given. Nay, we may go further with him, and look on the periotic bones as no part of the proper cranial wall, but as special developments within the otic capsule. But here we must stop, for neither anatomy nor development are reconcilable with the notions of the Okenian school respectina · the limbs of the head. Carus suggested, from the Okenian b point of view, that the premaxillro and maxillro must be cephalic ribs, and not cephalic limbs; but Rathke was the first to demonstrate that the inferior arche~ of the skull must be considered, if they are homologous with anything in the trunk, to partake of the nature of ribs rather than of that of limbs. But the confusion between analogy and affinity has led to such grave errors in the interpretation of the upper arches of the skull, that we must be upon our guard against running into similar mistakes with respect to the lower arches. It is easy enough to enumert\te four inferior arches to tho skull, just as there are four superior arches-the premaxjllm forming the first of these arches; the palato-pterygoid and maxillary apparatus, the second ; the mandible, with its suspensorium, the third ; the hyoidean arch, the fourth: and it might be plausibly enough represented that the first of these is united with the naBal segment of the skull, the second with the frontal segment ; while the third and fourth, being connected respectively with the anterior and the posterior parts of the periotic capsule, might be fairly considered to belong to the parietal and occipital segments. But do they really belong to those segtnents? and if so, why do they not remain attached to them ? What relation have the branchial arches to the skull, again? It is hard to see in what morphological character the first branchial arch of a fish differs from its hyoidean arch ; and if so, is it an arch of the skull, or an arch of the vertebral column? What, furthermore, are the original connections of the palato-pterygoid arch? Does it grow out of the mandibular arch from behind forwards, as Rathke seems to think; or has it, primitively, that connection with the prefrontal region which is so constant a character of the palatine bone ? THE THEOHY OF THE VERTEBHATE SKuLJJ. 303 These questions must be answered before the theory of th low~r arches of the skull can be placed upon as satisfactory ~ footing as that of the upper arches . and the . b I b tl b ' Y can e answered o~ y y 1e em ryologist, who may be encouraged to the difficult task by reflecting· on what he ha ~ d I d h • • • c. b one a rea y ; t ough keeping In VIew the adage of tho Roman, and UU "Nil actum reputans si quid superes. et agendum." |
