THE CENTRAL NERVOUS SYSTEM 761 



linking cortex with cortex, or central ganglia with each other. 

 In the third group are included (a) fibres which connect portions 

 of the cortex on the same side (association fibres) ; (b) fibres 

 which connect portions on opposite sides of the middle line 

 (commissural fibres) ; (c) fibres which connect the central grey 

 matter at diiferent levels e.g., the proprio-spinal or endogenous 

 fibres of the cord. Our first task is, therefore, to trace the 



Cerisi c ctl \ 



Enlargement V s - 



Sti llin gs Cervic a I 

 nucleus 



Cells of 



ct'fiterior 



Lumbar 



Enlargement q 



_ Z afe ral cell- colum n 

 (column of the tnter- 

 tnc die- lateral tract) 



- Shilling's dorsal 

 71 udeus or Clarke's 



Scattered cells of 

 inte r me die -latera 

 tract. 



FIG. 313. DIAGRAM OF GREY TRACTS OF CORD. 



peripheral nerves to their cells of origin or centres of reception* 

 in the nervous stem. And although there is reason to believe 

 that the whole of the peripheral nerves, cerebral and spinal 

 (with the exception of the olfactory and optic, which are rather 

 portions of the brain than true peripheral nerves), form a morpho- 



* The centre or nucleus of reception of a nerve contains the nerve-cells 

 around which its axons terminate ; the nucleus of origin of a nerve con- 

 tains the cells from which its axons arise. 



