1906-7.] Experimental Lesions in Motor Cortex of Monkey. 281 
XXIX.— Degenerations following Experimental Lesions in the 
Motor Cortex of the Monkey. By Sutherland Simpson, M.D., 
D.Sc., and W. A. Jolly, M.B. (From the Physiological Laboratory, 
University of Edinburgh.) Communicated by Professor E. A. 
Schafer, F.B.S. 
(MS. received July 5, 1907. Read July 15, 1907.) 
The object of the present research was to follow, by the degeneration 
method, the course of the fibres proceeding from definite and limited areas 
of the motor cortex, and to determine to what extent there is a grouping 
or localisation of the fibres of the pyramidal tract at different levels in the 
brain and spinal cord. 
The statement given in most text-books of anatomy and physiology 
that such a grouping exists in the internal capsule is based mainly upon 
experimental evidence obtained by Beevor and Horsley * in the macaque 
monkey and in the orang-outang. These observers found that on elec- 
trically exciting the capsule in transverse section no motor response could 
be obtained from the anterior limb or lenticulo-striate portion, but that 
the genu and the thalamo-lenticular portion of the posterior limb were 
excitable, and that definite movements were called forth by the stimulation 
of definite areas within these parts. From before backwards they found 
the fibres to be arranged in the following order : — farthest forward are 
situated those which control the movements of the eyes, then come those 
for the opening of the mouth, next those governing the movements of the 
head and eyes, and behind these the fibres for the tongue and the angle 
of the mouth. Just posterior to these lie the fibres for the anterior limb 
in the following order, — shoulder, wrist, fingers and thumb ; behind these 
come the trunk fibres, and most posterior of all those for the hind limb 
in the order of hip, ankle, knee, hallux, toes from before backwards. 
According to these observers, therefore, the arrangement of the fibres in 
the internal capsule is a reproduction of that of the areas on the cortex 
from which they arise, as determined by them.f The fibres situated at 
the genu of the capsule, i.e. farthest forward, come from the lowermost 
region of the motor cortex, behind them those from the middle region, 
and most posteriorly those from the uppermost portions of the motor area. 
* Beevor and Horsley, Phil. Trans. Roy. Soc. Loud., vol. clxxxi. B. (1890), p. 129. 
t Beevor and Horsley, loc. cit. (see fig. 7 in their paper). 
