456 



HANDBOOK OF PHYSIOLOGY. 



fibres, the prolongation from the cell by degrees assuming the character 

 of the nerve-fibre with which it is continuous. 



Ganglion-cells are generally inclosed in a transparent membranous 

 capsule similar in appearance to the nucleated sheath of Schwann in 

 nerve-fibres: within this capsule is a layer of small flattened cells. 



That process of a nerve-cell which becomes continuous with a nerve- 

 fibre is always unbranched as it leaves the cell. It at first has all the 

 characters of an axis-cylinder, but soon acquires a medullary sheath, and 

 then may be termed a nerve-fibre. This continuity of nerve-cells and 

 fibres may be readily traced out in the anterior cornua of the gray matter 

 of the spinal cord. In many large branched nerve-cells a distinctly 

 fibrillated appearance is observable; the fibrillae are probably continuous 

 with those of the axis-cylinder of a nerve. 



FIG. 316. 



FIG. 317. 



FIG. 316. Ganglion nerve-corpuscles of different shapes. (Klein and Noble Smith.) 

 FIG. 317. An isolated sympathetic ganglion cell of man, showing sheath with nucleated-cell lin- 

 ing, B. A. Ganglion-cell, with nucleus and nucleolus. C. Branched process. D. Unbranched pro- 

 cess. (Key and Retzius.) X 750. 



Any other points in the structure of nerve-cells will be mentioned 

 under the account of the different ganglia. 



II. FUNCTION OF NERVE-FIBRES. 



From the account of nervous action previously given it will be readily 

 understood (p. 428), that nerve-fibres are stimulated to act by anything 



