74 Historical Notices in regard to the Distinction of Nerioes 



for motion and for sensation, though these portions, he elsewhere main- 

 tains, ought rather to be considered as two distinct nerves than as the 

 twofold constituents of one. 



The proof of this is of various kinds. — In the first place, it is a theory 

 forced upon us hy the phenomena ; for only on this supposition can we 

 account for the following facts : — (1.) That we have distinct sensations 

 transmitted to the brain from differe^it parts of the same sensitive organ 

 (as the tongue) through which the same total nerve is diffused. (2.) 

 That we can send out from the brain a motive influence to one, nay, 

 sometimes to a part of one, muscle out of a plurality, among which the 

 same total nerve {c. g. the ischiatic) is distributed. (3.) That sometimes 

 a part is either, on the one hand, paralysed, without any loss of sensi- 

 bility, or, on the other, stupified, without a diminution of its mobility. 



In the second place, we can demonstrate the doctrine, proceeding both 

 from centre to periphery, and from periphery to centre. Though ulti- 

 mately dividing into filaments beyond our means of observation, we can 

 still go far in following out a nerve both in its general ramifications, and 

 in the special distribution of its filaments, for motion to the muscles and 

 for sensation to the skin, &c. ; and how far soever we are able to carry 

 our investigation, we always find the least fibrils into which we succeed in 

 analyzing a nerve, equally distinct and continuous as the chord of which 

 they were constituent. And again, in following back the filaments of 

 motion from the muscles, the filaments of sensation from the skin, we 

 find them ever collected into larger and larger bundles within the same 

 sheath, but never losing their individuality, never fused together to form 

 the substance of a larger chord. The nerves are thus not analogous to 

 arteries, which rise from a common trunk, convey a common fluid, di- 

 vide into branches all similar in action to each other and to the primary 

 trunk. For every larger nerve is only a complement of smaller nerves, 

 and every smallest nerve only a fasciculus of nervous fibrils ; and these 

 not only numerically different, but often differing from each other in the 

 character of their functions. 



In the third place, that in the nerves for both motion and sensation are 

 enveloped distinct nerves or fibrils for these several functions — this is 

 an inference supported by the analogy of those nerves which are motive 

 or sensitive exclusively. And in regard to these latter, it becomes im- 

 possible, in some cases, to conceive why a plurality of nerves should 

 have been found necessary, as in the case of the two portions of the 

 seventh pair, in reality distinct nerves, if we admit the supposition that 

 each nerve, each nervous fibril, is competent to the double office. 



In the fourth place, the two species of nerve are distinguished by a 

 difference of structure. For he maintains the old Galenic doctrine, that 

 the nerves of motion are, as compared with those of sensation, of a harder 

 and more fibrous texture, a diversity which he does not confine to the 

 homogeneous nerves, but extends to the counter filaments of the hetero- 

 geneous. This opinion, in modern times, by the majority surrendered 



