314 report — 1846. 



not at all against the recognition of a corresponding segment of the trunk, 

 though similarly composed. 



In fact, throughout this attack upon the vertebral theory of the skull, it 

 will be seen that it is based upon the a priori assumption that all the endo- 

 skeletal segments of the trunk, however modified, are vertebras, and all those 

 situated in the head, are not vertebrae. The essential character of a vertebra 

 is thus deduced from its position, not its composition. It needs only to com- 

 pare any of Cuvier's objections to the vertebral character of the cranial seg- 

 ments, with the modifications of the corporal segments admitted by him to 

 be vertebra?, previously enumerated in this Report (pp. 264-270), to see that 

 the characters of the cranial vertebra? objected to by Cuvier differ in degree not 

 in kind, and become valid arguments against the admittance of natural seg- 

 ments into the vertebral category, only when they happen to be situated at or 

 near the commencement of the series. 



It has been abundantly proved, I trust, that the idea of a natural segment 

 (vertebra) of the endoskeleton, does not necessarily involve the presence of 

 a particular number of pieces, or even a determinate and unchangeable ar- 

 rangement of them. The great object of my present labour has been to 

 deduce, by careful and sufficient observation of Nature, the relative value 

 and constancy of the different vertebral elements, and to trace the kind and 

 extent of their variations within the limits of a plain and obvious maintenance 

 of a typical character. 



In reference to the neural arch, the variation in the number and disposition 

 of its parts, illustrated in the figures 1, 2, 3,4, 18, 19, 20, 21, do not seem to 

 me, nor will they I apprehend to any unbiassed anatomist, to obliterate the 

 common typical character of that part of a vertebra. Those elements which 

 are furthest from the centrum are the chief seat of the changes. If the reader 

 will compare figure 2 with figure 19, he will see for example that the crown of 

 the arch is formed by a single bone(7) in the crocodile, but by two bones (7,7) 

 in fish ; nay, in most fishes the halves are even pushed apart by the interposi- 

 tion of a third bone. Yet the sagacity of Cuvier led him to determine the di- 

 varicated moieties of the divided parietal in such fishes to be the same (homo- 

 logous) bone with the single parietal of the crocodile. With what consistency, 

 then, can the general homology of the segments be rejected, which suffer no 

 other change in their composition than that resulting from the single or bifid 

 character of the same bone in each ? Is the single frontal of the human 

 adult regarded as a distinct bone from the bifid frontal of the foetus ? If, 

 therefore, the neural arch of the parietal vertebra (mesencephalic arch) of 

 the crocodile be free from the objection, raised by Cuvier to the vertebral 

 character of the homologous arch in man, on the score of the number of its 

 elements ; neither can that objection be allowed to have any force when it 

 rests upon the mere division in the human mesencephalic arch of the recog- 

 nised homologue of the single spinous element in the crocodile. 



In the sheep, the arch which encompasses the epencephalon is formed by 

 only three elements, the neural spine resting upon the conjoined upper ends 

 of the neurapophyses. In the dog these elements are divaricated and the 

 epencephalic arch is closed above by the neural spine. Now Cuvier does 

 not allow this difference of arrangement of the latter element (3) to affect his 

 recognition of the ' suroccipital ' in both mammals ; and, therefore, one is at 

 a loss to discover the consistency of the ideas which would repudiate the 

 general homology of the bones or of the entire arches which they surmount, 

 because, as Cuvier would say, " the composition of the arch is different, being 

 of three pieces in the sheep and of four pieces in the dog." Yet this is pre- 

 cisely the kind of objection which he has directed against the mesencephalic 

 arch, viz. because it may be composed of five or even six pieces, in certain 



