568 FUNCTIONS OF THE CEREBRO -SPINAL NERVOUS SYSTEM. 



structurally by actual division ; or functionally by the suspension of the 

 activity of other parts. In their state of perfect integrity and complete 

 functional activity, they are all (at least in Man) in such subordination to 

 the Cerebrum, that they only minister to its actions, except in so far as they 

 are subservient to the maintenance of the Organic functions, as in the auto- 

 matic acts of breathing and swallowing. With regard to every other action, 

 the Will, if it possesses its due predominance, can exercise a determining 

 power; keeping in check every automatic impulse, and repressing the 

 promptings of emotional excitement. And this seems to result from the 

 peculiar arrangement of the nervous apparatus ; which causes the excitor 

 impression to travel in the upward direction, if it meet with no interruption, 

 until it reaches the Cerebrum, without exciting any reflex movements in its 

 course. When it arrives at the Sensorium, it makes an impression on the 

 consciousness of the individual, and thus gives rise to a sensation; and the 

 change thus induced, being further propagated from the sensory ganglia to 

 the Cerebrum, becomes the occasion of the formation of an idea. If with 

 this idea any pleasurable or painful feeling should be associated, it assumes 

 the character of an emotion: and either as a simple or as an emotional idea, 

 it becomes the subject of intellectual operations, whose final issue is in a voli- 

 tional determination, or act of the Will, which may be exerted in producing 

 or checking a muscular movement, or in controlling or directing the current 

 of thought. 



458. But if this ordinary upward course be anywhere interruped, the im- 

 pression will then exert its power in a transverse direction, and a "reflex" 

 action will be tTie result; the nature of this being dependent upon the part 

 of the Cerebro-Spinal axis at which its ascent had been checked. Thus, if 

 the interruption be produced by division or injury of the Spinal Cord, so 

 that its lower part is cut off from communication with the encephalic centres, 

 this portion then acts as an independent centre; and impressions made upon 

 it through the afferent nerves proceeding to it from the lower extremities, 

 excite violent reflex movements, which, being thus produced without sensa- 

 tion, are designated as "excito-motor." So, again, if the impression should 

 be conveyed to the Sensorium, but should be prevented by the removal of 

 the Cerebrum, or by its state of functional inaction, or by the direction of 

 its activity into some other channel, from calling forth ideas through the 

 instrumentality of the latter, it may react upon the motor apparatus by the 

 "reflex" power of the Sensory ganglia themselves; as seems to be the case 

 with regard to those locomotive actions which are maintained and guided by 

 sensations during states of profound abstraction, when the attention of the 

 individual is so com pletely concentrated upon his own train of thought, that 

 he does not perceive external objects, although his movements are obviously 

 guided through the visual and tactile senses. Such actions, being depen- 

 dent upon the prompting of sensations, are "sensori-motor" or "consensual." 



But further, even the Cerebrum responds automatically to impressions 

 fitted to excite it to "reflex" action, when from any cause the Will is in 

 abeyance, and its power cannot be exerted either over the muscular system 

 or over the direction of the thoughts. Thus in the states of Reverie, Dream- 

 ing, Somnambulism, etc., whether spontaneous or artificially induced, ideas 

 which take possession of the mind, and from which it cannot free itself, may 

 excite respondent movements; and this may happen also when the force of 

 the Idea is morbidly exaggerated, and the Will is not suspended, but merely 

 weakened, as in many forms of Insanity. 



459. The general views here put forth in regard to the independent and 

 connected actions of the several primary divisions of the Cerebro-Spinal 

 apparatus, may perhaps be rendered more intelligible by the following 



