356 Miscellanea. 
The Cerebrum is universally admitted to be the portion of the nervous 
system which is instrumentally concerned in the formation of ideas, the 
excitement of the emotions, and the operations of the intellect; and there 
seems no reason why it should be exempted from the law of “reflex 
action” which applies to every other part of the nervous system.* And 
as we have seen that the emotions may act directly upon the muscular 
system through the motor nerves, there is ne a priori difficulty in believing 
that Ideas may become the sources of muscular movement, independently 
either of volitions or of emotions.—The relations of these different modes 
of action of the nervous system, and the place which this ideo-motor form 
of “ reflex” operation will hold in regard to the rest, will be made more 
apparent by the following tabular arrangement. 
+ — THE WILL} Volitional Movement 
Intellectual processes 
+ + 
pon a Crresrum+— Motor Impulse v 
: 
4 Ee 
5 & 
Ideas 3 2 
S 6 
Es 
Sensations —-——...-_ Sensory Ganoi1a-}— Motor Impulse | 3 
Impressions Sa SPINAL Corp. Motor Impulse 
Now if that ordinary wpward course of external impressions,—whereby 
they successively produce sensations, ideas, emotions, and intellectual pro- 
cesses, the will giving the final decision upon the action to which they 
prompt,—be anywhere interrupted, the impression will then exert its 
power in a transverse direction, and a “ reflex” action will be the result. 
This is well seen in cases of injury to the Spinal Cord, which disconnects 
its lower portion from the sensorium without destroying its own power; 
for impressions made upon the lower extremities then excite violent reflex 
actions, to which there would have been no tendency if the current of 
nervous force could have passed upwards to the Cerebrum. So, if sen- 
sations be prevented by the state of the Cerebrum from calling forth ideas 
through its instrumentality, they may react upon the motor apparatus 
in a manner which they would never do in its state of complete functional 
activity. This the Lecturer maintained to be the true account of the mode 
in which the locomotive movements are maintained and guided in states of 
profound abstraction, when the whole attention of the individual is so com- 
* To Dr. Laycock is due the credit of first extending the doctrine of 
reflex action to the Brain. 
