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the spinal column and the cranium, but that analogy becomes weaker 

 and weaker as we proceed towards the anterior end of the skull. 



Thus it may be right to say, that there is a primitive identity of 

 structure between the spinal or vertebral column and the skull ; but 

 it is no more true that the adult skull is a modified vertebral column, 

 than it would be, to affirm that the vertebral column is a modified 

 skull*. 



While firmly entertaining this belief, however, I by no means wish 

 to deny the interest and importance of inquiries into the analogies 

 which obtain between the segments, which enter into the com- 

 position of the ossified cranium, and the vertebrae of an ossified 

 spinal column. But all such inquiries must start with the recogni- 

 tion of the fundamental truths furnished by the study of develop- 

 ment, which, as our knowledge at present stands, appear to me to be 

 summed up in the following propositions : 



1 . The notochord of the vertebrate embryo ends in that region of 

 the basis cranii which ultimately lies behind the centre of the basi- 

 sphenoid bone. 



2. The basis cranii is never segmented. 



3. The lamina perpendicularis of the ethmoid has the same mor- 

 phological value as the presphenoid. 



4. The petrosal has the same morphological value as the mastoid ; 

 if one is not an integral part of the skull, neither is the other. 



5. The nasal bones are not neurapophyses. 



6. The branchial arches have the same morphological value as 

 the hyoid, and the latter as the mandibular arc. 



7. The mandibular arc is primitively attached behind the point of 

 xit from the skull, of the third division of the fifth nerve. 



8. The premaxilla is originally totally distinct from the palato- 

 maxillary arcade. 



9. The pectoral arch is originally totally distinct from the skull. 

 Starting on this basis, it might not be difficult to show that the 



perfectly ossified skull is divisible into a series of segments, whose 

 analogy with vertebrae is closer the nearer they lie to the occipital 

 region ; but the relation is an analogy and not an affinity, and these 

 cephalic sclerotomes are not vertebrae. 



* I feel sure that I met with this phrase somewhere, but I cannot recollect it& 

 author. 



