468 



ELEMENTARY PHYSIOLOGY 



or primitive slieath. In this way this process becomes 

 t!ie axis-cylinder of a medullated nerve-fibre, and is 

 continuous to the organ, usually a muscle, to which it is 

 distributed. 



The fact is, the distinction between the so-called nerve- 

 cell and the nerve-fibre is a wholly artificial one ; these 

 two, together with the nerve-ending, or a portion of it, 

 being all constituent parts of one cell, which is the real 

 unit of nervous architecture. This unit is termed the 

 NEURON. Every nerve-fibie then, whether within or 

 without the central nervous system, whether medullated 

 or non-medullated, is part of a neuron. 



Fia. 149. — Diagram of a Typical Cell from the Grev Matter of the 

 Spinal Cord. (Sherrinotok.) 



n, nucleus ; d, d, d, branched processes (dendrites) from the cell-body ; 

 p, pigment; c, part of cell-body which stains very readily (chromatin); 

 a, axis-cj'linder process, whicli acquires first a medulla, m, and then 

 (outside tlic cord) a neurilemma. 



A, represents the processes (dendrites) from a neighbouring cell inter- 

 lacing with, but not joined on to, the processes of the cell figured. 



The other cells of the grey matter are generally similar 

 in structure to the one described, though smaller than the 

 cells of the anterior horn. Certain of them however ex- 

 hibit particular features, on which we need not dwell here. 



The rest of the grey matter, apart from the neuroglia, 

 is made up of an interlacing network of naked (non- 



