1895.] Influence of Sensory Nerves upon Movement, tyc. 485 



root of the series is chosen for section ; namely, in the upper limb 

 the 8th cervical, and in the lower limb the 6th post-thoracic. (These 

 are the nerves that supply the skin over the whole of the hand and 

 foot respectively. It is to be remembered, however, that hand and 

 foot respectively are each of them supplied with sensation by at least 

 three sensory roots, the middle root covering the whole surface in 

 each case.) 



We attribute the fact that section of these large roots with their 

 wide distribution over hand and foot produces so little appreciable 

 effect, to the fact that the distribution of all the spinal nerves in the 

 skin is an overlapping one. The extent of overlapping is great 

 enough to prevent the section of any one nerve, even of the largest, 

 producing actual anaesthesia of the skin in any part. 



We further find that even if a field of absolute anaesthesia be 

 actually produced by section, for instance, of the 7th, 8th, and 9th 

 post-thoracic roots, or, in some cases, by section of the 7th and 8th 

 cervical and 1st and 2nd thoracic roots, the impairment of move- 

 ment resulting in the limb is comparatively slight. This is the 

 more remarkable when fche region deprived of sensibility includes 

 some of the most highly sensitive parts in the limb, namely, those of 

 the palm. 



In such a case the retention of sensibility, although in an impaired 

 degree, by the radial side of the palm, including pollex, is the cause, 

 in our opinion, of the remarkable quantity and quality of movements 

 still executed by the limb in spite of that impairment. In the case 

 of section of the 7th, 8th, and 9th post-thoracic sensory roots, it was 

 almost impossible, even on the closest examination, to detect any 

 defect of movement whatever ; the animal used both its feet appa- 

 rently equally well in climbing or running, there was no clumsiness 

 in picking up small objects (as a kernel) with the foot, and no 

 hesitation in so doing. The chief detectable muscular difference 

 between the limbs was that the knee-jerk was more brisk upon the 

 operated side, and the calf and ham and back of the thigh were very 

 deficient in sensation. 



In the case of section of the sensory roots of the 7th and 8th 

 cervical and 1st and 2nd thoracic, besides the ulnar border of the arm, 

 the hand, with the exception of the thumb and radial side of index, is 

 also quite insensitive ; and the sensitiveness of the skin of the thumb 

 and index, where present, is below normal in degree. Neverthe- 

 less, although impairment of movement (especially clumsiness) is 

 obvious, yet the condition is strikingly different to that obtaining 

 after the whole series of roots has been cut through. Food is 

 easily taken up from the hand and picked up from the floor with the 

 thumb and index of the partially apaesthete limb, and the limb is 

 freely used in progression and in climbing. The grasp of the partially 



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