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Proceedings of the Royal Society of Edinburgh. [Sess. 
By the degeneration method Melius * * * § found that fibres from the hallux 
and thumb centres, after passing through the corona radiata, enter the 
internal capsule towards its posterior extremity, while those from the face 
area enter it at its anterior extremity. As they pass downwards the leg 
and arm fibres become displaced forwards, while those from the face area 
are displaced backwards, until in the lower levels of the capsule the fibres 
from all three areas are crowded together in the middle third of the posterior 
limb. In the movement of the facial fibres backwards between the upper 
and lower planes of the capsule at a certain level they will be found at the 
genu, the position which they are usually said to occupy, but above this par- 
ticular level they are in front of, and below it they are behind, the genu.f 
In the cerebral peduncle the area occupied by the fibres of the pyramidal 
tract | in transverse sections is variously given by different authorities, 
and also the relative positions of the fibres amongst themselves. They are 
often described as occupying the middle third of the crusta, the leg fibres 
lying most external, the face fibres most internal, and the arm fibres 
between. Van Gehuchten § ascribes to them the middle three-fifths of the 
crusta. Stanley Barnes, j| in several cases where the whole of the fibres 
from the Rolandic area had been interrupted, found that the fibres 
in the middle region of the crusta were all degenerated ; the inner two- 
fifths (the fronto-pontine region) and the outer one-sixth (the temporo- 
pontine region) were in the main free, but the distinction between the 
degenerated and the undegenerated regions was not sharp, the two sets 
of fibres intermingling at the junction. 
In the monkey, Melius H found that the pyramidal fibres take up the 
middle third of the crusta, and that the face fibres are mixed up with those 
from the leg and arm areas and do not occupy a space to themselves mesial 
to the latter. 
Regarding the arrangement of fibres in conducting tracts generally in 
the spinal cord Sherrington ** in 1893 pointed out that for the ascending 
* Melius, Proc. Roy. Soc. Lond. (1894), vol. lv. p. 208, and (1895) vol. lviii. p. 206. 
t In the literature the term “ internal capsule ” is very loosely applied. In every case 
where a lesion or degeneration of the capsule is described its exact horizontal level should 
be given. 
I Strictly speaking, the term “ pyramidal tract ” should be applied only to those fibres 
which pass to the spinal cord and govern the movements of the trunk, arm and leg, but by 
most writers it is used in the most comprehensive sense, and includes all the projection 
fibres arising from the motor cortex. 
§ Yan Gehuchten, Systeme nerveux de Vhomme, 4th ed. (1906), p. 907. 
II Stanley Barnes, Brain , vol. xxiv. (1901), p. 464. 
II Melius, loc. cit. 
** Sherrington, Jour, of Physiol., vol. xxiv. (1893), p. 298. 
