298 Proceedings of the Poyal Society of Edinburgh. [Sess. 
terminate in a copious fine degeneration. One or two similar fibres are 
visible on the homolateral side. In longitudinal sections of this segment 
they are seen to come off at right angles from the main tract and to 
enter the grey matter. These fibres are more numerous and more easily 
followed in this specimen than in any that we have examined. 
The degeneration does not cease at the lower end of the cervical enlarge- 
ment, but is continued down through the thoracic and lumbar segments 
as a few sparsely scattered fibres both on the crossed and on the uncrossed 
side. A few isolated fibres on the crossed side are still present in the last 
sacral segment. 
Degeneration following Limited Lesions. 
In addition to the above, limited lesions were made within each of the 
larger motor areas, and the degenerations traced from these. Within the 
leg area the following centres were located by stimulation, and small 
portions of the cortex, including them, were cauterised — centre for extension 
of hallux and toes (in two animals), for flexion of knee and for flexion 
of hip (one each). Within the arm area four lesions were made, involving 
the centres for rotation of arm at shoulder, for flexion of wrist, and for 
flexion of fingers (two cases) ; and within the face area the centre for the 
opening of the mouth was destroyed. 
We shall not attempt to describe the degeneration in detail in each 
case. It is sufficient to say that below the level of the mid-brain there 
is no evidence of any localisation of the fibres within the area of the 
pyramidal tract in transverse sections. In the pons, medulla oblongata, 
and spinal cord they are practically evenly distributed over this area, 
the only difference between the effects of an extensive and a limited lesion 
being in the density of the degeneration, i.e. in the number of fibres 
degenerated. Following all lesions of the arm area some fibres can be 
traced to the lumbar region of the spinal cord, and in all lesions of the 
leg area some appear to terminate in the cervical enlargement. In the 
case of the limited lesion within the face area some fibres pass into the 
pyramidal tract of both sides of the cord, crossed and uncrossed, and can 
be followed to the 2nd thoracic segment, but not beyond it. 
In the lower levels of the internal capsule and in the crusta the fibres 
from the hip, knee and digits centres are scattered fairly evenly over those 
segments of the pyramidal tract which degenerate after extirpation of 
the entire leg area ; that is to say, no localisation of fibres within the leg 
area can be made out with certainty in these regions. The same applies 
to the fibres from the circumscribed lesions within the arm and face areas. 
