FUNCTIONS OF SPINAL NERVES. 139 



The anterior fascicles of the cord and the anterior roots 

 of the nerves which proceed from them are insensible, and 

 produce muscular contraction. The posterior fascicles of the 

 cord, and the posterior roots of the nerves, have no motor 

 power, but they are sensitive. Each spinal nerve, formed by 

 the union of the anterior and posterior roots, contains sensi- 

 tive filaments and motor filaments placed side by side in its 

 trunk and its ramifications. It follows, therefore, that these 

 nerves and their subdivisions are mixed; as regards the 

 composition of their fascicles, they are at once sensitive and 

 motor. They are sensitive to mechanical irritation, and they 

 excite muscular contraction under the influence of galvanism, 

 for both these agents meet in the same nerve-filaments 

 subject to their power. These filaments, separately con- 

 sidered, come from the centre to the periphery without 

 division and without anastomosing, in the exact sense of the 

 word, for what is called anastomosis of the nerves is a simple 

 juxtaposition, proximity without exchange of their proper 

 substance, and without intimate fusion. 



It is to the continuity of the nervous filaments, and to their 

 independence, that distinctness of tactile sensation and pre- 

 cision of motion is due. It is clear, therefore, that if two 

 sensitive filaments should unite their proper substance, the 

 impressions perceived by them previous to their union would 

 be confounded, and would not be referred by the brain to 

 distinct points. If, for example, two filaments running to 

 the index and middle fingers, were united, instead of being 

 simply placed side by side, at any point between the finger- 

 tips and the brain, they would carry to the brain but one 

 single sensation for both fingers, and it would be impossible 

 to tell upon which one the impression had been made. The 

 result would be the same if two filaments of a motor nerve 

 running to these fingers were united, instead of isolated in 

 their proper substance; the motor impulse would be trans- 

 mitted to both fingers alike, and the brain could not move 

 either expressly. 



In persons who have suffered amputation, phenomena are 

 produced which are explained by the fact that all the fila- 

 ments of a nerve exist at its origin which are found at its 



