The Excitable Cortex of the Chimpanzee, Oranrr-rtan, and Gorilla 193 



Some of the degenerated fibres were anionrj those that entered the pyramidal 

 decussation in the headmost portion of the decussation. In the spinal cord, 

 at a level midway between 1st and 2nd cervical r(K)t3,a heavy degeneration 

 exists in the pyramidal rogion of both lateral colunms. but is heavier in the 

 riirht than in the left. In both the degeneration extends out to the extreme 



At 



edge of the lateral column for the greater part of the periphery of the 

 column, but is absent from it at the dorsal angle of the column, where it 



Fig. 22.— Outlines ( x 3 nat. size) of cross-sections of the bulb and spinal cord of 

 chimpanzee, showing the pyramidal-tract degenerations following lesion in the 

 arm area of both hemispheres in ablation-experiment 2. 



scarcely at all invades an area of large nerve-fibres (dorsal cerebellar tract). 

 The main degeneration lying in the deeper part of the lateral column joins 

 the zonal part of the degenerated area by a narrowish isthmus. A small 

 degeneration exists in each ventral column alongside the deeper half of the 

 lip of the ventral fissure. A segment lower the configuration of the 

 degenerations in cross-section has altered, in that a zonal area in the dorsal 

 half of each lateral column exists free from degenerated fibres. By the 

 level of the 7th cervical segment the amount of degeneration has obviously 

 lessened ; it is clearly less heavy in the left half of cord than in the right. 

 In each lateral column it reaches the periphery over a limited small stretch 

 about the junction of the ventral third with the dorsal two-thirds of the 



