FUNCTIONS OF NERVE-FIBRES. 481 



But (as Volkmann shows) it must not be assumed, as it 

 often has been, from these examples, that the mind has no 

 power of discriminating the very point in the length of any 

 nerve-fibre to which an irritation is applied. Even in the 

 instances referred to, the mind perceives the pressure of a 

 nerve at the point of pressure, as well as in the seeming 

 sensations derived from the extremities of the fibres : and 

 in stumps, pain is felt in the stump, as well as, seemingly, 

 in the parts removed. It is not quite certain whether those 

 sensations are perceived by the nerve-fibres which are on 

 their way to be distributed elsewhere, or by the sentient 

 extremities of nerves which are themselves distributed to 

 the many trunks of the nerves, the nervi nervorum. The 

 latter is the more probable supposition. 



The habit of the mind to refer impressions received 

 through the sensitive nerves to the parts from which im- 

 pressions through those nerves are, or were, commonly 

 received, is further exemplified when the relative position 

 of the peripheral extremities of sensitive nerves is changed 

 artificially, as in the transposition of portions of skin. When 

 in the restoration of a nose, a flap of skin is turned down 

 from the forehead and made to unite with the stump of the 

 nose, the new nose thus formed has, as long as the isthmus 

 of skin by which it maintains its original connections re- 

 mains undivided, the same sensations as if it were still on 

 the forehead ; in other words, when the nose is touched, 

 the patient feels the impression as if it were made on the 

 forehead. When the communication of the nervous fibres 

 of the new nose with those of the forehead is cut off by 

 division of the isthmus of skin, the sensations are no longer 

 referred to the forehead ; the sensibility of the nose is at 

 first absent, but is gradually developed. 



When, in a part of the body which receives two sensitive 

 nerves, one is paralysed, the other may or may not be in- 

 adequate to maintaim the sensibility of the entire part; the 

 extent to which the sensibility is preserved corresponding 



