378 
NAT ORE 
[August 20, 1885 
enables the muscle fibre to contract and so cause movement of 
one or more muscles. Now, with this idea of the general plan 
on which the whole nervous system is constructed, you will 
understand that muscular action, ze. movement, will occur in 
proportion to (1) the intensity of the stimulation of the sensory 
corpuscle ; and (2) the resistance in the different channels. 
When a simple flow through the whole apparatus occurs, it is 
called a simple reflex action, and this was discovered in Eng- 
land by Dr. Marshall Hall. 
To recapitulate : a nerye centre, theoretically speaking, we 
find to consist of a sensory corpuscle on the one hand and a 
motor corpuscle on the other, both these being united by june- 
tion threads or commissures, To such a centre come sensations 
or impressions from the nerve-endings, and from such a centre 
go out impulses which set the muscles in action. 
I haye dwelt thus at length on this most elementary point, 
because it appears to me that, in consequence of the rapidity 
with which function is being demonstrated to be definitely 
localised in various portions of the cerebral hemispheres, we are 
in danger of losing sight of Dr. Hugblings Jackson’s grand 
generalisations on nerye function, and that we are gradually 
inclining to the belief that the function of each part is very dis- 
tinct, and therefore can most readily act without disturbing 
another part. 
In fact, we are perhaps drifting towards the quicksands of 
spontaneity, and disregarding entirely the facts of every-day life 
which show that every cycle of nerve action includes a disturb- 
ance of the sensory side as well as the active motor agency. 
Did we in fact admit the possibility of the motor corpuscle 
acting Zev se, and in the absence of any sensory stimulation we 
should again be placed in the position of believing that an effect 
could be produced in the absence of a cause. 
For these reasons such a centre has been termed kinesthetic 
or sensori motor, and such centres exist in large quantities in the 
spinal cord, and they perform for us the lower functions of our 
lives without arousing our consciousness cr only the substrata of 
the same. 
But now, turning to the brain, although I am extremely 
anxious to maintain the idea just enunciated that, when discuss- 
ing the abstract side of its functions we should remember the 
sensori motor arrangement of the ideal centre, I shall have to 
show you directly that the two sides—namely, the sensory and 
motor—in the brain are separated by a wide interval, and that 
in consequence we have got into the habit of referring to the 
groups of sensory and motor corpuscles in the brain as distinct 
centres. I trust you will not confuse these expressions, this 
unfortunately feeble terminology, and that you will understand, 
although parts may be anatomically separated and only connected 
by commissural threads, that functionally they are closely 
correlated. 
In consequence of the bilateral symmetry of our bodies we 
possess a double brain—a practically symmetrical arrangement 
of two intimately connected halves or hemispheres which, as 
you know, are concerned with opposite sides of the body, for 
the right hemisphere moves the left limbs, and wrce versd. 
For my purpose it will be sufficient if we regard the brain as 
composed of two great collections of gray matter or nerve cor- 
puscles which are connected with sensory nerve-endings, with 
muscles, and intimately with one another. 
In this transverse section of a monkey’s brain, which is stained 
dark blue to show up its ccmponent parts, you will see all over 
the surface a quantity of dark gray matter, which is simply the 
richly convoluted surface of the brain cut across. Observe it is 
about a quarter of an inch deep, and frcm it lead downwards 
numerous white fibres down towards the spinal cord. The sur- 
face of the brain, the highest and most complicated part of the 
thinking organ, is called the cortex, bark, or rind, and in it are 
arranged the motor centres I am about todescribe. These white 
fibres coming away from it to the cord, not only are channels 
conveying messages down to the muscles, but also carrying 
messages from the innumerable sense corpuscles all over the 
body. 
So much for one grey mass of centres. Now down here at 
the base of the brain you see two lumps or masses of the same 
nature, and these are called, therefore, the basal ganglia or grey 
masses. Since they are placed at the side of the paths from the 
cortex, and undoubtedly do not interfere with the passage of 
impulses along those paihs, we may put them aside, remember- 
ing that they probably are concerned with low actions of the 
nervous system, such as eating, &c., which are popularly termed 
automatic functions. 
1 
In this photograph of a model made by Prof. Aeby, of Berne, 
you see represented from the front the two cerebral hemispheres 
with the centres in the cortex as little masses on the surface, and 
the basal ganglia as darker ones at the bottom, while leading 
from them down into the spinal cord are wires to indicate the 
channels of communication. 
Note, in passing, that both hemispheres are connected by a 
thick band of fibres called the ‘‘corpus callosum.” It is, I 
believe, the close union thus produced between the two halves 
that leads in a great measure (though not wholly) to consonance 
of ideas. 
The arrangement of the fibres will be rendered still clearer by 
this scheme, in which the cortex is represented by this concave 
mass, and the fibres issuing from the same by these threads, 
The basal ganglia would occupy this position, and they haye 
their own system of fibres. 
I will now leave these generalisations, and explain at once the 
great advance in our knowledge of the brain that has been made 
during the last decade. The remarkable discovery that the 
cortex or surface of the brain contained centres which governed 
definite groups of muscles, was first made by the German ob- 
servers Hitzig and Fritsch ; their results were, however, very 
incomplete, and it was reserved for Prof. Ferrier to produce a 
masterly demonstration of the existence and exact position of 
these centres, and to found an entirely new scheme of cerebral 
physiology. 
The cortex of the brain, although it is convoluted in this 
exceedingly complex manner, fortunately shows great constancy 
in the arrangement of its convolutions, and we may therefore 
readily grasp the main features of the same without much 
trouble. 
From this photograph of the left side of an adult human 
brain you will see that its outer surface or cortex is deeply 
fissured by a groove running backward just below its middle, 
which groove is called the ‘‘ fissure of Sylvius,” after a dis- 
tinguished medizeval anatomist. ‘his fissure, if carried upwards, 
would almost divide the brain into a motor half in front and a 
sensory half behind. , 
Of equal practical importance is another ‘deep fissure which 
runs at an open angle to the last, and which is called the “‘ fissvre 
of Rolando,” Rolando being another pioneer of cerebral topo- 
graphy. Now it is around this fissure of Rolando that the motor 
side of the centres for voluntary movement is situated; and 
when this portion of the cortex is irritated by gentle electric 
currents, a constant movement follows according to the part 
stimulated. / 
Because of their upward direction, the conyolutions bounding 
the fissure of Rolando are called respectively the ‘‘ascending 
frontal” and ‘‘ ascending parietal” convolutions. 
Now here, at the lowest end of the fissure of Rolando, we 
find motor areas for the movement of both sides of the face: 
that is to say that, as regards this particular piece of the cortex, 
it has the power of moving not only its regular side of the face, 
the right, but also the left—that, in fact, both sides of the face 
move by impulse from it. ae 
Higher up we find an area for movement of the opposite side 
of the face only, I reserve for a moment the description of this 
portion of the b:ain, and pass on to say that above these centres 
for the face we find the next is for the upper limb, and most 
especially the common movement of the upper limb—viz. grasp- 
ing, indeed the only forward movement which the elbow is 
capable of, namely, flexion. The grasping and bringing of an 
object near to us is the commonest movement by far, and we 
find here that this centre is mainly concerned in it. Behind 
the fissure of Rolando Dr, Ferrier jlaced the centres for the 
fingers. : 
Next above the arm area is a portion of the cortex which 
moves the lower limb only, and in front of this again is an area 
for consonant action of the opposite arm and leg. ‘ 
Let me here remind you that this being the left hemisphere, 
these are the centres for movement of the opposite, that is, the 
right limbs, and that in the other hemisphere there are corre- 
sponding areas for the left limbs. 
Thus here we have mapped out those portions of the cortex 
which regulate the voluntary movement of the limbs. So far I 
have omitted mention of the muscles of the trunk, namely, 
those which move the shoulders, the hips, and bend and 
straighten the back, Dr. Ferrier had shown that there existed 
on the outer surface of the cortex, here, a small area for the 
movement of the head from side to side. 
Prof, Schafer and myself have found that the large trunk 
