1906-7.] Experimental Lesions in Motor Cortex of Monkey. 297 
crossed fibres is about the same as that following extirpation of the 
entire motor area. 
In the spinal cord most, but not all, of the fibres of both the homo- 
lateral and the crossed pyramidal tracts terminate in the grey matter of 
the cervical enlargement ; a few can be traced to the lower end of the 
sacral region. This is a point worthy of note, because the lesion in this 
case certainly did not encroach upon the leg area. 
Degeneration following Extirpation of the Face Area. 
In this case the lesion is not confined to the face area, but extends into 
the adjacent arm area to some extent. It includes the cortical centres for 
the opening of the mouth and for the movement of the larynx, upper lip, 
eyelids, neck and digits (see fig. 1). The association and commissural 
fibres were not followed. The degeneration in the internal capsule covers 
an area somewhat more extensive than that following extirpation of the 
arm centre alone, and its anterior extremity lies farther forwards ; beyond 
this there is nothing worthy of special notice. 
In the mesencephalon it occupies about three-fifths of the crusta (fig. 4), 
its inner limit approaching nearer to the middle line than in the case of 
the arm lesion. Scattered fibres are found on the mesial and lateral 
aspects of the main mass of degeneration, but the outer extremity of the 
latter (temporo-pontine) segment is quite free. Fibres pass into and 
terminate in the substantia nigra, but in this case none can be followed 
into the tegmentum. 
In the pons the only point calling for special mention is the relatively 
large amount of fine degeneration which is scattered amongst the cells of 
the grey matter surrounding the pontine pyramidal bundles. This is more 
abundant on their mesial aspect than on their lateral, but it ends abruptly at 
the median raphe. A few scattered fibres are found in the inner portion 
of the mesial fillet. In the lowermost levels of the pons a few isolated 
fibres leave the posterior aspect of the pyramidal bundles and can be traced 
backwards through the fine degeneration to the fillet, where they disappear. 
In the medulla oblongata the degeneration is scattered over the whole 
area of the transverse section of the pyramid, but it is slightly denser in 
the mesial portion than in the lateral. The ratio of crossed to uncrossed 
fibres in the first cervical segment just below the decussation is about 
100 : 1, and it remains the same throughout the spinal cord. 
Spinal Cord. — In the lower part of the cervical enlargement numerous 
fibres are seen to pass obliquely in from the crossed pyramidal tract and 
to enter the grey matter at the base of the posterior horn, where they 
