330 BIOLOGICAL PHYSICS 



by osmosis, the materials required for nerve nutrition, 

 while the collateral, or parietal, dendrons, extend horizon- 

 tally, by continuations of the cell wall, it may be, in 

 union, or interlacement, with those of neighbouring cells ; 

 thus forming a supporting structure, or framework, apart 

 from, but in conjunction with, the neuroglial, fibro-cellular, 

 and unorganised substance, or glial cement. 



The cells being thus fixed, and nourished, grow in a 

 direction opposite to their apical, or radical, terminations, 

 viz. in the direction of the axis cylinders, or axons, issuing 

 from them, and thence continuously, by peripheral ex- 

 tensions, until the first synapse, or the first intercepting 

 ganglionic cells are encountered, or interjected, in their 

 course, until they terminate as motor fibres in the various 

 muscular structures of the body, and limbs, until they 

 end in the sense organs, or in the general peripheral 

 cutaneous nerve endings, or until, by communicating 

 filaments to the sympathetic nervous system, they end 

 within the parenchyma of the various organs, or on the 

 free surfaces of the various cavities, or hollow spaces, of 

 the body. 



The form of neuron, here described, may be regarded 

 as, typical, or characteristic, of all the neurons individually, 

 which go to make up the structure of the systemic nervous 

 system as a whole. 



The nerve cell of the cortex cerebri, varies in size, and 

 shape, according to its position, depth, etc. ; the nerve cell 

 of the lower centres, is also characterised by variety of 

 size, and shape, differences of function, and relationship, 

 probably being the determining causes of this. The nerve 

 substances, entering into the axonal structures of a 

 neuron, are divided into medullary, and non-medullary, 

 the latter consisting of the axis cylinder, the central, and 

 conducting, part, of the nerve mechanism, an axilemmar, 

 or containing, sheath, surrounded by the former, the 

 " white substance of Schwann," with its containing sheath, 

 or neurilemma. 



The cell is, thus, the investing substance, in which the 

 true nerve elements, the nuclei, and nucleoli, and axonal 

 fibres, are developed, and maintained, and, in, and from, 

 which they grow, its chief function being that of select- 



