THE PHYSIOLOGY OF THE SENSE OF TOUCH 161 



They are also found in monkeys (Quain). The distribution 

 of these touch corpuscles is significant ; thus, there have 

 been found on the ventral surface of the index-finger as many 

 as twenty-one to the square centimetre, whereas in other parts 

 of the palm and sole they vary from two to eight to the square 

 centimetre. This is in keeping with the well-known sensitive- 

 ness of the pulps of the index-finger. It may be well to quote 

 here the observations of Weber as to the dehcacy of discrimina- 

 tion in different regions of the human body. 



He examined the sldn with a pair of compasses, noting the 

 distances between their points, when they were still felt as two 

 points in such regions as the tongue and different parts of the 

 limbs. Some of his results were : 



Tip of tongue, -^ in. or 1 mm. 



Palmar surface of terminal phalanx of forefinger, ^^ in. or 2 mm. 



Palmar surface of middle phalanges of fingers, ^ in. or 4 mm. 



Palm of hand, -^ in. or 10 mm. 



Dorsal surface of first phalanges of fingers, --^ in. or 14 mm. 



Dorsum of hand, 1^ in. or 25 mm. 



Upper and lower parts of forearm, 1 J in. or 37 mm. 



Middle of thigh and back, 2| in. or 62 mm. 



He also found that the points of the compasses had to be 

 separated further so as to be felt as two, in the hmbs, when the 

 hue joining the points was in the long axis of the Umbs, than 

 when placed transversely. 



Relations between the Papillary Ridges and Papilla} of the 

 Corium. — The foregoing drawings and photographs show clearly 

 a close connection between these two structures, and httle 

 needs to be added to what has been said before. Wherever 

 ridges are clearly cut and well formed, there is always a corre- 

 sponding development of the papillae of the corium, and this 

 is particularly noticeable in the Carnivores, the Lemuridse 

 and Monkeys, and most of all in Man. The relation is so close 

 and so seldom departed from, that I venture to affirm that 

 the old term papillary ridges, with the meaning it coimotes, 

 ought to be retained as indicating a constant relation between 

 two great structures of the skin, and a sound physiological 

 theory. 



