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Proceedings of the Royal Society of Edinburgh. [Sess. 
tion of the fibres, but the arrangement was different from that found by Gad 
and Flatau. 
Sherrington,* on the other hand, in the monkey, found only slight 
evidence of any localisation of fibres within the pyramidal tract in the spinal 
cord. After extirpation of the more mesial and anterior parts of the 
motor cortex (leg and trunk areas presumably), the most marked degenera- 
tion of the crossed pyramidal tract was to be found bordering the dorsal 
cerebellar tract, while, on the other hand, this region was only slightly 
affected when the extirpation was in the more lateral and posterior parts 
of the motor cortex (arm and face areas). Otherwise the degeneration 
was scattered uniformly over the whole field of the transverse section of 
the tract. 
Melius t found, similarly, that after lesions in the hallux and thumb 
centres the degeneration in the crossed pyramidal tract in the cord was 
evenly scattered over its entire area. The thumb centre, however, he 
located behind the fissure of Rolando, in the post-central convolution, — a 
region which is now believed to lie outside the motor area. 
Thus, according to those observers who have employed the physiological 
method of direct electrical excitation, there would appear to be a definite 
grouping of the fibres within the pyramidal tract in the internal capsule 
and in the spinal cord, corresponding to the grouping of nerve cells in the 
cortex from which these fibres arise. Tested by the anatomical or degenera- 
tion method, on the other hand, the statements are conflicting, and with 
regard to the spinal cord the majority of observers have found that no 
such grouping exists. 
Methods employed. 
In our experiments we have used monkeys — Macacus rhcesus chiefly — 
and a few specimens of callithrix. In each case the animal was com- 
pletely anaesthetised with ether, the scalp, after being shaved and cleansed 
with carbolic acid and alcohol, was incised, a skin flap turned down, and 
a trephine opening made in the skull over the fissure of Rolando. This 
opening was then enlarged with bone forceps. After reflection of the dura 
and exposure of the cortex, the centre to be extirpated was located by 
stimulation with a weak faradic current, Sherrington’s unipolar method 
being employed in the manner described by us in a former communica- 
tion. I A small portion of the cortex embracing the centre located was 
* Sherrington, Jour, of Physiol ., vol. x. (1889), p. 429. 
f Melius, loc. cit. 
+ Proc. Roy. Soc. Edin., vol. xxvii., pt. i., p. 64. 
