THE SKELETON OF THE VERTEBRATE HEAD. 109 



embryological, and general relations, indicate, I believe, their 

 real nature as parts of the neuro-skeleton. . 



The most complex and important development of the ac- 

 tinapophyseal elements of the sclerome are those arrange- 

 ments which constitute the framework of the limbs. As, 

 however, I find myself compelled to dissent from Professor 

 Owen's determination of the anterior pair of limbs as the 

 haemal arch and " divergent appendages" of the occipital ver- 

 tebra ; and as I also dissent from his general doctrine of 

 limbs, I shall reserve my observations on the subject for a 

 separate communication. 



The osseous formations in connection with the subintegu- 

 mentary fibrous lamina constitute collectively the dermal por- 

 tion of the sclerome. As the constitution of the exo-skeleton 

 does not immediately bear on the object I have in view, I 

 shall merely observe, in reference to it, that a more extended 

 and systematic investigation of its structure and morphology 

 is at present very much to be desired. 



From the statements already made, it will be observed 

 that I consider that the most general conception we can at 

 present reach of a vertebra or sclerotonie, is a somewhat ex- 

 panded or detailed form of Von Baer's ideal transverse section 

 of the vertebrate animal, which is based on the original 

 neural and haemal foldings of the blastoderma from the sides 

 of the corda dorsalis. With reference to the further develop- 

 ment of the idea, I venture to express my decided opinion, 

 that formally to announce the archetypal number of elements 

 in a segment of the skeleton is a premature attempt at gen- 

 eralisation, and that a dogmatic statement on a subject of this 

 kind must have a greater tendency to check legitimate induc- 

 tion the higher the authority from which it emanates.. 



The modifications which occur in the Sclerotomes towards or 

 at the front of the Head. It is generally admitted, that in 

 tracing backwards the series of sclerotomes in a vertebrate 



