1895.] following Unilateral Lesions of the Cortex Cerebri. 207 



inferior genu of the fissure of Rolando ; fine fibres only passed to the 

 superior parietal lobule ; degenerate fibres, mostly fine, were traced 

 to the posterior portion of the superior frontal convolution ; both 

 coarse and fine to the lobulus paracentralis ; fine only to the 

 precuneus, and a very little fine degeneration to the gyrus fornicatus. 

 The degenerate fibres crossing in the corpus callosum were very fine 

 and occupied the middle third of its antero-posterior extent. This 

 corresponded very closely with the antero-posterior extent of the 

 ascending parietal convolution at this level. Degenerate fibres could 

 be traced into the convolutions of the right hemisphere corresponding 

 to the distribution of the degeneration in the left, but considerably 

 less in amount, and the area of distribution being rather less exten- 

 sive. Both coarse and fine degenerate fibres, varying considerably in 

 amount in different animals, pass from the lesion through the mesial 

 half of the centrum semiovale to the left internal capsule, in the lower 

 levels of which they are located in the middle third of the posterior 

 limb. From the internal capsule most of the fine degeneration passes 

 into the optic thalamus. In the left cms the degeneration is very 

 evenly scattered over the middle third, and many coarse degenerate 

 fibres pass from here into the substantia nigra. At the decussation of 

 the pyramids the tract divides, the larger portion crossing to the oppo- 

 site lateral column while the smaller goes to that of the same side (vide 

 Preliminary Report*). The amount of degeneration passing to the 

 lateral column of the same (left) side varies from a third of all the 

 degeneration in one case to about a twentieth in the other two. In 

 each case a small number of degenerate fibres remain in the left 

 anterior column after the completion of the decussation. The amount 

 varies in different cases and is not apparently dependent on the 

 proportion of degenerate fibres passing to the lateral column of the 

 same side. The relations and extent of the degenerated areas remain 

 unchanged throughout the cervical and dorsal cord. The degenera- 

 tion in the crossed tract of each side is evenly scattered over its entire 

 area, the two sides only differing in the density of the degeneration. 



In the upper cervical region the tendency of the crossed tract to 

 mingle with or encroach on the boundaries of the direct cerebellar 

 tract is well illustrated. In the lumbar region the degeneration in 

 each crossed tract and in the left anterior column (Tooth) begins to 

 go out, and in the only case examined at that level the degeneration 

 had not all disappeared at the level of the third sacral root. 



Degeneration following Lesions of the Thumb Centre. 



The portion of cortex removed in these cases was from the 

 ascending parietal convolution between the lower extremity of the 



Koy. Soc. Proc.,' 1894. 

 VOL. LVIII. Q 



