io8 THE SPINAL CORD AND CEREBELLUM 



or lumbar portions important centres are to be found 

 for the digestive and renal organs. 



This carries us one step further, but here our diffi- 

 culties really begin. We may be able to specify the 

 kinds of impulses which are likely to proceed from 

 the digestive organs by analyzing the various forms 

 of action of that region. We may group them with 

 reference to their course by the motor and sensory 

 roots of the spinal nerves with at least a certain 

 degree of probability ; but when we enter the spiaal 

 cord itself, and seek to trace the paths they follow 

 and the nerve- cells with which they are connected, we 

 tread upon ground where exploration, though actively 

 pursued, has as yet yielded but, comparatively speak- 

 ing, few definite results, 

 other In addition to the direct and crossed pyramidal 



tracts. 



tracts there are a few scattered fibres in the latter of 

 these, to which the term idiolateral pyramidal tract 

 has been applied. The reason for this is that a 

 cerebral lesion in one hemisphere will give rise simul- 

 taneously to degeneration, not only in the direct and 

 crossed pyramidal tracts, but in the crossed pyramidal 

 tract of the same side as the hemisphere affected.* 

 In the posterior column, besides the outer portion 

 called Burdach's column, and the inner portion called 

 Goll's column, there is a small tract, more centrally 

 placed, spoken of as the ' descending comma tract.' 

 It is supposed to be composed — at least in part — of the 

 descending portions of the posterior root- fibres which 

 * Foster, loc. cit., p. 942. 



