EXTRACT XXIII. 

 ON OSSIFICATION, AND THE SKELETON. 



OSSIFICATION, as an embryonic and early foetal, his- 

 tological process, begins, after the differentiation of the 

 neurenteric canal, and the early evolution of the structures, 

 springing from the areas, respectively innervated by the 

 sympathetic and systemic nervous systems, and pro- 

 gresses, in the first instances, mainly by cartilaginous 

 modes of solidification, of certain definite points, or small 

 areas, of, the then, entirely soft tissues, such as, the bases 

 of the future units of the vertebral column, and the basi- 

 sphenoid, para-chordal and trabecular, cartilages. 



This earliest example of the process synchronises with 

 the appearance, and functional activity of the notochord, 

 and seems due to the distribution of earthy material lime 

 salts especially by that, then, prominent embryonic 

 structure, to the fibro-cellular matrix of the future 

 vertebral bodies, and spheno-chordal basal tissues the 

 physical union of the two skeletal evolutionary elements, 

 protoplasmic, and earthy, their structural solidification, as 

 cartilage, and their subsequent conversion into bone, by 

 absolute ossification, following as the terminal result. 



When this earliest skeletal provision has become effected 

 to the extent, that the future systemic neuro-musculature, 

 can obtain sufficient support, solid points of attachment, 

 and protection, to develop itself throughout the areas of 

 sympathetic innervation, the process of ossification is 

 repeated, at points corresponding with what are called 

 " centres of ossification," throughout the whole skeletal 

 areas of the, calvarium. body and limbs of the developing 



