50 
DR. C. E. BEEVOR AND MR. V. HORSLEY ON THE EXCITABLE 
that, when the destination and function of these fibres is fully known, this term 
will be abandoned with great advantage for a specific topographical nomenclature. 
At present, however, we must use the old expression in default of a better one. 
In previous investigations (‘Phil. Trans., B., 1887, 1888) we have described the 
foci^ of representation in the cortex cerebri of the Macacque Monkey {Macacus sirdcus), 
of the movements of the chief divisions of the body. 
It remained for us to see whether there were issuing from such foci bundles of 
fibres conveying the functional impulses originating in those foci, and whether such 
fibres were arranged, as has been suggested by one of us (‘ Lancet,' July, 1884), in an 
order similar to that which prevails on the surface of the cortex. 
From what has been already done in this matter it is evident that the problem can 
be attacked in two difterent ways, either by stimulation of the motor fibres of the 
internal capsule, or by removing difterent parts of the so-called motor cortex, and 
tracing downwards the degeneration produced in the motor fibres through the internal 
capsule and crus cerebri. 
In this present paper, we have employed only the former of these tAvo methods, 
viz., electrical stimulation of the fibres of the internal capsule, as exposed in horizontal 
section of the hemisphere. Some knowledge of the arrangement of the fibres in the 
internal capsule has already been gained by experimental and anatomical research, 
and the facts as known at the present time we will now summarise. 
HISTORICAL 1NTRODUCTIOX. 
Previous writers, on this question, have investigated the subject by several methods 
in difterent kinds of animals, viz.. Rodents, Carnivora, Monkeys, and Man. The 
methods employed were for the most part anatomical, or consisted in tracing paths of 
degeneration. Very rarely has excitation been resorted to. Considering the varied 
mode in which movement is represented in the cortex of the brain in difterent animals, 
we have thought it best to arrantre the facts we have deduced from the above 
researches under the headings of the various species of the animal examined, in the 
order already given. 
Birds. 
PiTREst found that in Pigeons and Chickens ablation of a hemisphere produced no 
descending degeneration. 
Marii'iaals. 
liodents. 
PiTREst found that in the Guinea Pig and Rabbit destruction of the excitable parts 
* By the term “focus’’ we mean the point where the movements of any given segment are most 
intensely represented. 
t ‘ Comptes Rendos de rAcademie des Sciences,’ vol. 9d, July, 1884, p. 89. 
