MOTOR AND SENSORY NERVES. 537 



inherent in the same fibres or belong to fibres physiologically distinct and derived from 

 different parts of the central system. This question, which was solved only about half a 

 century ago, will be the first to engage our attention. 



Distinct Seat of the Motor and Sensory Properties of the Spinal Nerves. All of the 

 nerves that take their origin from the spinal cord are endowed with motor and sensory 

 properties. These nerves supply the whole body, except the head and other parts 

 receiving branches from the cranial nerves. They arise by thirty-one pairs from the 

 sides of the spinal cord, and each nerve has an anterior and a posterior root. The ana- 

 tomical differences between the two roots are that the anterior is the smaller and has no 

 ganglion. The larger, posterior root presents a ganglionic enlargement in the interver- 

 tebral foramen. Just beyond the ganglion, the two roots coalesce and form a single 

 trunk. The nerve-fibres in the two roots are not of the same size, the anterior fibres 

 measuring on an average about one-fourth more than the posterior fibres. The structure 

 of the ganglia of the posterior roots has already been considered sufficiently in detail. 



It wonld be unprofitable to discuss the vague ideas of the older anatomists and physi- 

 ologists with regard to the properties of the roots of the spinal nerves, and we can 

 date our information upon this point from the suggestion of Alexander Walker, in 1809, 

 that one of these roots was for sensation alone and the other for motion. It is most 

 remarkable, however, that Walker, from purely theoretical considerations, should have 

 stated that the posterior roots were motor and the anterior roots sensory, precisely the 

 reverse of the truth, and should have advanced this view in a publication as late as 

 1844. In the work alluded to, which contains some of the most extraordinary pseudo- 

 scientific vagaries ever published, it is curious to see how near Walker came to the great- 

 est discovery in physiology since the description of the circulation of the blood. 



It is unnecessary to enlarge upon the importance of the discovery that the anterior 

 roots of the spinal nerves are motor, and the posterior, sensory, and that the union of 

 these two roots in the mixed nerves gives them their double properties, for we can hard- 

 ly imagine a physiology of the cerebro-spinal nervous system without this fact as the 

 starting-point. In an article published in English, in October, 1868, 1 and in French, 

 during the same year, 2 we have given an elaborate review of the whole subject, being 

 prompted to do so by the perusal of what purported to be an exact reprint of the origi- 

 nal pamphlet by Charles Bell. This pamphlet was printed for private circulation, in 

 1811, and was never published. It has been entirely inaccessible, and its contents were 

 only to be divined by references and quotations in the subsequent writings of Sir Charles 

 Bell and of his brother-in-law, Mr. Shaw. 



Physiological literature d^es not present another instance of the merit of a great dis- 

 covery resting upon references to an unpublished pamphlet, which no student could pos- 

 sibly consult in the original, none of these references, upon close analysis, proving to be 

 entirely distinct and satisfactory. It is not to be wondered at, therefore, that, in our 

 study of the origin of one of the greatest discoveries of all ages, a reprint of the original 

 memoir should be examined with the most critical care. That this reprint was correct, 

 seemed probable from a comparison of its text with the quotations from the original to 

 be found in the writings of Sir Charles Bell and Mr. Shaw, and from the testimony of 

 reviewers who claimed to have compared it with the original. Within a short time, 

 however, an authorized reprint in full, from a manuscript in the hands of the widow of 

 the author, has appeared in the Journal of Anatomy. 



When the only reprint of the celebrated pamphlet of Sir Charles Bell was itself exces- 

 sively rare, we thought it desirable to make long quotations to indicate the ideas enter- 

 tained by Bell regarding the properties of the two roots of the spinal nerves ; but, now 



1 FLINT, JR., Historical Considerations concerning the Properties of the Roots of the Spinal Nerved Quar- 

 terly Journal of Psychological Medicine, New York, 1868, vol. ii., p. 025, et seq. 



2 Journal de Fanatomie, Paris, 1868, tome v., p. 520, etseq., and p. 575, et seq. 



