336 Dr*. C. 8. Sherrington. On the Fibres of [Dec. 8, 



from the sensory roots it is easy to show that the skin of the 1st digit 

 is segmentally anterior to that of the 2nd digit, that of 2nd to that of 

 3rd, and so on. The skin of the dorsum of the foot is shown to be 

 segmentally anterior to the sole. 



The nipple lies in the middle of the 4th thoracic field, but is also 

 included in the fields of the 3rd and 5th thoracic. The umbilicus is 

 in the llth thoracic root field. 



The number of segments entering into the composition of the skin 

 of the limb is seen to be greater than the number of segments con- 

 tributing to its musculature. To the skin of the anterior aspect of 

 the fore-limb, six segments contribute (3rd, 4th, 5th, 6th, 7th, 8th 

 cervical) ; to that of the hind-limb six segments also (1st, 2nd, 3rd, 

 4th, 5th, 6th post- thoracic). To the posterior part of the fore-limb 

 four segments contribute (1st, 2nd, 3rd, 4th thoracic) ; to that of the 

 hind-limb four segments also, (6th, 7th, 8th, 9th post- thoracic). 



In each limb the anterior aspect is segmentally more extensive than 

 the posterior. I have shown that this last fact is exemplified even 

 more strikingly in the musculature of each. limb. 



The quadrifid or quinquifid digital partition at the fr.ee end of the 

 limb gives no indication of the number of segmental skin fields in it. 



Joints such as knee and ankle, which might perhaps seem natural 

 boundaries marking fundamentally distinct portions of the limb, are 

 not regarded as such in the segmentation of the cord, as evidenced 

 by posterior roots. 



The absolute segmental level of a point of surface is subject to in- 

 dividual variation, as was shown to be the case with muscular points 

 in the substance of the body wall and viscera. This individual varia- 

 tion affecting the skin corresponds with variation in the constitution 

 of the efferent roots ; the limb plexus may be postfixed or prefixed 

 by its sensory spinal roots, just as it may be by its motor spinal 

 roots. A mixed nerve may be postfixed by its motor roots and by its 

 sensory in the same individual, or may be prefixed by both. But 

 there is some evidence (Frog) that a. plexus may be prefixed by its 

 motor roots when it is not so by its sensory roots, and vice versa. 



The distribution of the fibres of the sensory spinal root in the limb, 

 as elsewhere, indicates a segmental significance in their constitution 

 rather than a functional based upon coordination. Without denying 

 the existence of functional factors in the progressive development of 

 the limb, it must be admitted that there is little evidence that the 

 collection of fibres in each sensory root has resulted from an assort- 

 ment of the fibres with a view towards assisting in functional co- 

 ordination. 



Peyer's statement of the correspondence of locality of the muscular 

 and cutaneous distributions of a spinal nerve does not apply in the 

 Monkey. The 9th post- thoracic nerve innervates the intrinsic 



