PHYSIOLOGY AND PATHOLOGY OP THE BRAIN. 
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in regular lines — the posterior columns going to the optic tha- 
lami, and the anterior to the corpora striata. So far they were 
distinct and separate; but from the bodies just named, minute 
fibres were given off, which mingled together, and could be 
traced to the cortical substance, where they terminated : the 
medullary part of the brain is made up of these fibres, running 
between the cortical substance and the optic and striated bodies. 
The examination of various animals shews a correspondence 
between the quantity of this cortical substance and the depth 
of its convolutions, 8cc., and the intelligence of the animal. 
Experiments have clearly shewn, that on slicing away the brain, 
there is no indication of suffering ; but the animal becomes 
more dull and stupid in proportion to the quantity of cortical 
substance removed. Where disease commences at the circum- 
ference of the brain, the mental faculties are always affected 
first ; but where it commences in the central parts of that 
organ, the mental faculties are the last to become affected. 
These and several other facts, warrant him in considering the 
cortical substance of the brain as the seat of intelligence, and 
therefore by means of the fibres forming the medullary portion, 
the influence of volition is transmitted from the grey matter to 
the corpora striata, and impressions on the external organs of 
sense are conveyed from the optic thalami to the grey substance. 
In other words, the medullary fibres running between the cor- 
tical substance and the corpora striata, transmit the influence of 
volition to the motor column ; and those running between the 
optic thalami and the cortical substance, transmit impressions 
from the sensitive column to the mind. 
But there are various movements continually going on in the 
frame, with which volition has nothing to do, and with the very 
existence of which we are in a great measure or altogether un- 
conscious, — such is action of the various muscles connected with 
organic life. All motion is occasioned by stimuli acting upon 
muscular contractility, and these may be classed under two 
heads — the stimulus of volition, and that of chemical and me- 
chanical agents. This is the difference between voluntary and 
involuntary motion ; and with this important circumstance, that 
the voluntary muscles often act independently of the will, and 
even in direct opposition to its mandates. 
These involuntary motions belong to the system called, by 
Dr. Marshall Hall, “ Excito-motory.” In voluntary motion, the 
impression having beerrrnade, its influence is conveyed to the 
part acted upon by means of the same motor nervous filament 
throughout. The involuntary action is produced by means of a 
reflex function, — the impression is first made on a sensitive 
