THE SPINAL CORD AND CEREBELLUM 97 



cerebelltim and groups of muscles — Anatomical relations 

 of the cerebellum — Eelations of the cerebellum to the 

 spinal cord — Beohterew's classification — Brief summary of 

 the pathological evidence — Development of the cerebellum 

 — The chemical or nutritive influence of the cerebellum 

 in eq^uilibration — The cerebellum as a reinforcing organ — 

 Its relations to the vaso-motor centre — Does the cerebellum 

 influence chemical action directly? — Chemical action as a 

 constant element in nervous activity. 



It is essential at this stage to call to mind some of '^^^ oi^ief 



features of 



the chief features of the spinal cord. Though, roughly the spinal 

 speaking, of a circular shape, it is divided like the brain 

 itself into two halves. This division, which is not 

 absolute, is caused by an anterior and a posterior 

 fissure, the latter the deeper of the two, being in 

 reality a septum or membranous partition rather than 

 a fissure. Each half is made up of a more or less 

 central portion consisting mostly of nerve-cells and 

 a peripheral or external portion composed chiefly of 

 nerve-fibres. These fibres are divided throughout the 

 whole length of the cord into three main columns — 

 the anterior, lateral, and posterior. Issuing from the 

 cord between the vertebrae at slightly irregular dis- 

 tances proceed on each side the spinal nerves by two 

 roots, the anterior root passing out from the anterior 

 horn through the anterior column, whilst the posterior 

 root divides the posterior from the lateral column. 



The spinal nerves are mainly channels of sensory 

 and motor impulses, and they differ greatly in size in 

 accordance with that of the parts they supply, those 

 which are distributed to the arms and legs being very 



7 



