THE SPINAL CORD AND CEREBELLUM 99 



possibly, it is thought, in the sacral region also* and 

 in the bulb above the spinal cord. These cells, it is 

 held,t are not connected with the motor fibres which 

 go to muscles nor with the ordinary sensory fibres, 

 although they do receive fibres from the posterior or 

 sensory roots, as we shall presently see in greater detail. 

 Besides the three great divisions before mentioned the 

 white matter is divided into numerous tracts. The 5^*°'^.™ 



the white 



posterior column is divided by a septum into the matter. 

 postero-median and postero-external columns. Sepa- 

 rated from the last-named by the fibres of the dorsal 

 root is the cerebellar tract, which, throughout rather 

 narrow, stretches forward along the margin of the 

 cord almost to its anterior surface. Between this 

 and the gray matter lies the crossed pyramidal tract, 

 whilst following the margin of the cord forward from 

 the cerebellar tract we have the antero-lateral ascend- 

 ing tract with the antero-lateral descending tract, and 

 the direct pyramidal tract at its extremity bordering 

 on the anterior fissure. Of these tracts, three — the 

 median posterior, the cerebellar, and the antero-lateral 

 ascending — are termed ascending to signify that they 

 are supposed to carry impulses upwards to the brain, 

 whilst three — the crossed and direct pyramidal and 

 the antero-lateral descending — are called descending 

 tracts for a corresponding reason, t 



The connections and functions of some of these 

 tracts are but partly known. Fairly well defined, 



* Foster, loc. cit., pp. 956-958. 

 + Ihid., p. 958. X Ibid., p. 945. 



7—2 



