CENTRAL NERVOUS SYSTEM. 



173 



PART I.— PHYSIOLOGY OF THE NERVE-CELL. 



A. Anatomical Characteristics of the Nerve-cell. 



Form of Nerve-cells. — Morphologically the mature nerve-eel 1 is regarded 

 as composed of a cell-body, containing a nucleus, together with other modified 

 inclusions, and possessed of one or more outgrowths or branches. Some of 

 these branches may be very long, such, for instance, as those which form 

 nerve-fibres ; other branches are short and differ from the nerve-fibres in 

 their structure. 



The terms employed in describing the nerve-elements are as follows : To 

 the entire mass under the control of a given nucleus and forming both cell- 

 body and branches, the term neurone is applied. The inclusions within the 









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Fig. 67. — A group of human nerve-cells, all drawn to the same scale, from pioparations according to 

 Nissl's method, made by Dr. Adolph Meyer, and kindly furnished for this purpose; X 300: a, small motor 

 cell from ventral horn of cervical spinal cord ; b, cell from " Clarke's column," thoracic cord ; c, small 

 nerve-cell from tip of dorsal horn, thoracic cord ; d, spinal ganglion-cell, cervical root ; > . three granules 

 from the granular layer of the cerebellum; /, l'urkinje's cell from the same preparation as « ; <i, small 

 pyramidal cell from the second layer of the cerebral cortex of the central gyri ; It, giant pyramidal cell 

 from the same region. 



cell-body have the usual designations. Nerve-cells differ greatly in the 

 number of the branches arising from them. In some cells there appear t<> be 

 two nerve-fibres arising from the cell-body, in others, only one. For conve- 

 nience the descriptions about to be given will apply to the latter group only. 

 From most cells there arises one principal branch, which when considered 

 alone is described as a nerve-fibre, but when considered as the outgrowth of 

 the cell-body from which it originates is called the axone. The axone, in 

 many cases, has branches, both near its origin from the cell-body and also 

 along its course. These branches are designated as collaterals. At their 

 distal ends the main stem of the axone and also the collaterals subdivide 



