ON THE VERTEBRATE SKELETON. 311 



Cuvier seeks to obscure by the normal absence of its proper transverse pro- 

 cesses in man, and the assumed transference of them to another part of the 

 skull. 



Cuvier in the next place objects to the comparison of the supraoccipital 

 with the neural spine of a trunk- vertebra, " because of its vast difference of 

 structure and function." He does not specify the nature of the difference : 

 he admits that the neural spines have distinct centres of ossification in certain 

 animals ; and all will allow that, in most of the trunk-vertebrse of such, the 

 neural canal is closed by the coadapted ends of the neurapophyses to which 

 the spine articulates or becomes anchylosed : that therefore such spine does not 

 directly cover the neural axis, but, retaining the shape signified by its name, 

 performs exclusively the function in relation to muscular attachments. At 

 first view the contrast seems conclusive against all homology between such 

 mere intermuscular spine and the broad thin convex plate applied over the 

 cerebellum and posterior cerebral lobes in man. And it must be confessed 

 that the determination of their general homological relations could not have 

 been satisfactorily demonstrated by the mere relations of the parts to the 

 laminae supporting them, in so limited a range of comparison. But, if we 

 descend to the fish, we shall find the supraoccipital equally excluded from 

 the neural canal by the meeting of the exoccipitals beneath its base ; we 

 shall, also, see it still retaining the spinous figure, indicating its function in 

 relation to muscular attachments to predominate over that in subserviency 

 to the protection of the epencephalon. If we next ascend to the crocodile, 

 we shall find the neural spine of the atlas to be one of those examples alluded 

 to by Cuvier, where the ossification proceeds from an independent centre : 

 and it not only thus manifests its essential character as an autogenous ver- 

 tebral element, but maintains its permanent separation from the neurapo- 

 physes : and it further indicates the modifications of form to which the cor- 

 responding elements will be subject in the more expanded neural arches of 

 the antecedent cranial segments by having already exchanged its compressed 

 spinous for a depressed lamellar form. Here indeed Cuvier might not only 

 have objected to recognise it as a vertebral spine by reason of its change of 

 form and function, but also by its continuing a distinct bone, which is 

 not the case with the expanded ' spine ' of the mammalian occipital vertebra. 

 But returning to the crocodile, we observe in the segment anterior to the atlas 

 that both the form and connections of the supraoccipital (fig. 22, 3) are 

 so closely similar to those of the neural spine of the atlas that the recog- 

 nition of their serial homology is unavoidable ; and we have a repetition 

 of the same characters of the vertebral element in question in the small and 

 undivided parietal (ib.i'). Now Cuvier makes no difficulty in admitting the 

 ' occipital superieur ' in the crocodile to be the homologous bone with its 

 more expanded namesake in the bird; or this with the still more expanded 

 ' partie grande et mince de l'occipital ' in mammals and man : he is also 

 disposed to admit the special homology of the supraoccipital under all 

 its variations of form and function in the above-cited air-breathing animals 

 with the bone 3 in fishes, which he sometimes calls ' occipital superieur,' 

 sometimes 'interparietal.' If then the special homology be admitted on the 

 ground of the constancy of the connections of the part, with what show of 

 reason can its general homology be rejected which forms the very basis or 

 condition of the characters determinative of such admitted special homology ? 

 But Cuvier is not consistent with himself in his grounds of objection to the 

 essential nature of the human supraoccipital as the neural spine of its seg- 

 ment ; for he does not hesitate to call the atlas of the crocodile a vertebra, 



