328 INNERVATION. [CHAP. XI. 



of the existence of two orders of fibres ; nor do they add anything 

 to our knowledge beyond the important fact, that actions take 

 place in invertebrata after decapitation which are of the same 

 nature with those which occur in vertebrata after a similar mutila- 

 tion. The mechanism of these actions has not been at all elucidated 

 by these experiments. 



Respecting the second hypothesis, we must remark, that it is 

 just as competent to explain the phenomena of decapitated animals, 

 as paralysed limbs, as that of Dr. Hall, and that it receives some 

 support from the almost universal concurrence of sensation with 

 those normal actions which Dr. Hall would attribute to excito- 

 motory fibres. If it be supposed that these fibres have a certain 

 relation to the gray matter of the spinal cord, there can be no good 

 reason against the further supposition, that they may continue to be 

 affected by it after the brain has been separated from the cord. 

 This hypothesis, however, is liable to the same objections as that of 

 excito-motory fibres : it is inadequate to explain the influence of 

 emotion on paralysed limbs, and the paralysis of the sphincters ; and,' 

 moreover, it cannot be considered to be proved that fibres are con- 

 tinued up directly from the spinal nerves to the brain. The fibres 

 of the anterior pyramids, no doubt, are true cerebro-spinal fibres ; 

 but they may be merely commissural. We have no evidence that 

 fibres of the lumbar region of the cord pass into the brain. The 

 longitudinal course of fibres in the spinal cord affords no proof that 

 those fibres pass into the brain, for it is well known that most of the 

 nerves take a very oblique course from their point of separation from 

 the cord to their emergence from the spinal canal ; and it is pro- 

 bable that the fibres continue their obliquity in the cord itself, so 

 that their real origin would be higher up than their apparent one. 

 This great length of oblique course gives to the fibre the appear- 

 ance of being strictly longitudinal, whereas it may be implanted in 

 the gray matter of the cord. 



The third hypothesis appears to us to admit of fewer objections 

 than either of the others, and to be more consonant with what 

 seems to be the correct anatomy of the cord. It supposes that the 

 mechanism of a mental and that of a physical nervous action are es- 

 sentially the same, differing only in the nature and the mode of 

 application of the stimulus. The same afferent and efferent fibres are 

 exerted in the one case as in the other ; the former acting as sen- 

 sitive or excitor, or both; the latter as channels for voluntary, 

 emotional, or strictly physical impulses to emotion. 



This hypothesis is content to assume that fibres of sensation and 



