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Proceedings of the Royal Society of Edinburgh. [Sess. 
as far as the 4th sacral segment (fig. 16) and the crossed (heterolateral) 
tract, to the first coccygeal segment. Fibres entering the grey matter can 
be seen in the lumbar region, as in the cervical enlargement, ending in 
fine degeneration in a similar position. 
The ratio of the heterolateral to the homolateral fibres remains about 
the same in the different levels of the spinal cord from the upper cervical 
to the lower sacral region ; it is approximately 40 to 1 in this particular 
animal. An eyepiece micrometer ruled in squares was used to estimate the 
number of degenerated fibres in the two respective areas, but no great 
degree of exactitude can be claimed for the enumeration. The area of 
degeneration and the number of degenerated fibres diminishes most rapidly 
from the 5th cervical to the 1st thoracic segment, and again from the 3rd 
lumbar to the 1st sacral segment. In all sections of the spinal cord 
numerous sound fibres are scattered amongst the degenerated ones. 
Fig. 16. — Fourth sacral. 
In all sections examined above the spinal cord a few degenerated fibres 
are found in the area of the pyramidal tract on the side opposite to that 
of the lesion. They diminish from above downwards both absolutely and 
relatively to those of the other (homolateral) side, until in the anterior 
pyramid, just above the decussation in the medulla oblongata, only six or 
eight can be counted. In the internal capsule the proportion of fine to 
coarse fibres is greater than in the crusta and pontine bundles. The fine 
degeneration ends chiefly in the adjacent lateral nucleus of the optic 
thalamus. 
In another animal an attempt was made to cauterise the whole motor 
area, but on the post-mortem examination it was found that the cortex 
