1096 CUTANEOUS SENSATIONS. [BOOK in. 



tracts in the spinal cord, these tracts apparently keeping always 

 to the same side, the great majority pass to the cerebellum ; and 

 of these again the greater number, all those along the cerebellar 

 tract, and some of those passing through the gracile and cuneate 

 nuclei remain uncrossed to the end. The only path by which 

 all these impulses thus passing to the cerebellum can gain 

 access to the cortex of the cerebrum, is by some or other of the 

 ties between the cerebellum and the cerebral cortex. The rela- 

 tively few impulses which pass along the fillet are for the most 

 part landed in the middle parts of the brain, for only a small 

 portion of the fillet passes to the cortex ( 634), and it is not 

 clear that this part of the fillet comes from the gracile and 

 cuneate nuclei, so that most of these impulses can gain access to 

 the cortex only by the relays of these middle parts of the brain. 



Very striking indeed are these constant relays along the path 

 of sensory impulses ; in this respect the sensory impulses offer a 

 strong contrast to the motor impulses. But a still more complex 

 system of relays has to be mentioned ; for yet a third path is open 

 for sensory, afferent impulses along the cord. We must admit the 

 possibility of afferent impulses travelling along the network of the 

 grey matter, their path being either absolutely confined to the 

 grey matter, or leaving the grey matter at intervals, and joining 

 it again by means of those, longer or shorter, commissural or 

 internuncial fibres which unite the longitudinal segments of grey 

 matter, arid form no inconsiderable portion of the whole white 

 matter of the cord. We have seen ( 586) that under abnormal 

 circumstances, impulses pass freely in all directions along the grey 

 matter, and we may conclude that under normal circumstances 

 they can pass along it, under restrictions and along lines deter- 

 mined by physiological conditions. The fibres in the white matter 

 which do not shew either descending or ascending degeneration 

 are, probably, as we have said ( 581), internuncial fibres, con- 

 necting segments of grey matter in a longitudinal direction ; and, 

 though we have no exact knowledge touching this matter, we may 

 suppose that some of these convey impulses upwards, and others 

 downwards. 



If, as some maintain, the fibres of the ascending antero-lateral 

 tract end not in the cerebellum, but in the grey matter of the 

 bulb, or higher up, we have a fourth path for sensory impulses, 

 which after the primary relay in the segmental grey matter pass 

 straight up to the bulb. 



681. How do experimental results and clinical histories 

 accord with such an anatomical programme ? 



We may first call attention to an experiment, which though 

 somewhat old, carried out on rabbits, and confined to one region 

 only of the cord, the lower thoracic, has nevertheless a certain value 

 on account of its affording more or less distinctly quantitative and 

 measurable results. We have seen, 175, that afferent impulses 



