332 INNER VATION. [CHAP. XI. 



roots of the nerves exhibit no difference of structure ; no anatomist 

 could distinguish in a compound nerve the sensitive from the motor 

 filaments. The vesicular matter, however, in the anterior horn, 

 contains large caudate vesicles of a remarkable and peculiar kind 

 (fig. 56, p. 214) ; whilst that in the posterior horn resembles very 

 much the vesicular matter of the cerebral convolutions, and of other 

 parts of the cerebrum, and does not contain caudate vesicles, except 

 near the base. Here, then, we find associated with the well-attested 

 difference in the functions of the anterior and posterior roots, a 

 striking difference in the structure of the anterior and posterior 

 horns of gray matter. 



This hypothesis is adequate to the explanation of the influence of 

 emotion on limbs paralysed as to voluntary movement, without the 

 necessity of assuming the existence of a totally distinct series of 

 fibres for this class of actions. The change in the brain, excited by 

 emotion, is propagated to the spinal gray matter, in a manner analo- 

 gous to that in which the influence of the will is brought to bear 

 on it. It thus affects the ordinary motor fibres ; and, therefore, 

 the movements which are produced by emotion resemble very 

 closely those excited by the will. 



This hypothesis suggests a very obvious explanation of the kind 

 of antagonism which appears to exist between voluntary and reflex 

 actions. It is well known that in health the will can in a great de- 

 gree control and prevent the development of reflex actions in the 

 lower extremities. If one be paralysed, as in hemiplegia, from disease 

 of the brain, whilst the other remains sound, a very striking contrast 

 is sometimes to be observed between the two limbs. On stimulating 

 the sole of the foot in the diseased limb, reflex actions are readily 

 produced ; but, on applying the same stimulus to the same part of 

 the sound limb, no such movements occur, the patient being con- 

 scious of the .application of the stimulus, but resisting the tendency 

 to action which it produces. The will has lost its control over the 

 diseased limb ; but, as the motor nerves and the spinal gray matter 

 are sound, actions may be still excited through a stimulus from the 

 periphery ; and, the more complete has been the separation of the 

 brain's influence from the cord, the more perfect will be the reflex 

 actions. Hence we frequently find these movements more perfect 

 in cases where sensation as well as voluntary power is destroyed 

 in a limb, than where the latter only has ceased. 



It may be here remarked, that movements which at one time 

 are voluntary, may at another time be physical. If the influence of 

 the will be suspended for a brief period, stimulation of the surface 



