Royal Society. 67 



The principal results at which the author has arrived are as fol- 

 lows : — 



That the posterior roots of the spinal nerves consist of three kinds ; 

 two of these enter the posterior grey substance at right angles, and 

 the third kind with different degrees of obliquity upwards, a small 

 proportion of the latter taking a longitudinal course and becoming 

 lost in the posterior white columns. 



That in no instance were any of the fibres of the anterior roots 

 seen to ascend with the anterior white columns, before they entered 

 the grey substance. 



That besides the transverse bundles that form the anterior roots, 

 a continuous system of exceedingly fine transverse fibres issue from 

 the anterior grey substance and become lost as they proceed towards 

 the surface of the chord. 



That from the preceding facts, it may be inferred that nearly all, 

 if not the whole of the fibres composing the roots of the spinal nerves 

 proceed at once to the grey substance of the chord ; and that if any 

 of them ascend directly to the brain, it must be those only of the 

 posterior roots which run longitudinally in the posterior white 

 columns. 



That the communication between the sensorium and the spinal 

 nerves is not established by the posterior white columns, but by the 

 antero-lateral columns, especially the lateral. 



That many of the fibres which belong respectively to the anterior 

 and posterior roots in different regions of the chord, terminate there 

 by forming with each other a series of loops of various sizes and 

 lengths ; and that it is not improbable that some of them may reach 

 even as far as the brain, as it is well known that the formation of 

 loops is one mode in which nerve-fibres do terminate there. A por- 

 tion of the roots however may be connected with the vesicles of the 

 chord, although the evidence of any such connection is very un- 

 satisfactory. 



That there are reasons for believing that the grey substance of 

 the chord does not transmit impressions to and from the brain ; and 

 that the fine longitudinal fibres described by Stilling have not been 

 found by the author. 



That there is a great correspondence in the fibrous arrangement 

 between the grey substance of the chord and the chiasma of the 

 optic nerves. That the fact that the nerve-roots not only diverge 

 both upwards and downwards to a considerable distance beyond 

 their point of entrance, but intermingle also with each other in the 

 most intricate manner, may explain how impressions made at one 

 particular spot are communicated in different directions to distant 

 parts of the chord, so as to excite a simultaneous and sympathetic 

 action in classes of muscles which otherwise would appear uncon- 

 nected. 



April 21. — Extract from a letter from M. Kamtz addressed to 

 Colonel Sabine (Translation). 



Dorpat, 15th March (N. Style), 1853. 



1 have just completed the memoir on terrestrial magnetism which 



F2 



