The Excitable Cortex of the Chimpanzee, Oiang-Utan, and Gorilla 217 



althoUL'h facial, linirual, brachial, and hind-limb movements of the contra- 

 lateral side were evoked to«:ether by stimulation anvwliere in the cross- 

 section of the tract at that level, the movements in face and tongue 

 predominated greatly when the electrode was applied to the mesial portion 

 of the cut face of the tract, and movements of toes when the application 

 was to the outer lateral portion of the tract, while, when the electrode lay 

 about midway between the mesial and lateral borders of the tract, there 

 was marked predominance of the finger movements (tig. 30, B). The 

 inference is therefore that although by that level the pyramidal-tract 

 fibres from face, arm, and leg areas have become a good deal commingled 



Fig. 30. — A, outline of cross-section of tlie crura cerebri in a large orang, to show the position of the 

 spots in the crusta whence unipolar faradisation elicited separable movements of opposite side. 



1, movement of toes and ankle ; 2, hip ami knee ; 3, abilomiiial wall and chest wall ; 4, fingers, thumb, and wrist ; 

 5, face and tongue ; between 3 and 4, movements of elbow, wrist, and shoulder. 



B, outline of cross-section of anterior part of pons of gorilla, to show points whence move- 

 ments predominating in toes (t), in fingers and thumb (/), and in face (F) respectively were 

 elicitable by unipolar faradisation. 



those for face predominate toward the mesial side of the tract, those for 

 leg towards the lateral, and those for arm in the middle part of the tract's 

 cross-area. 



Along with these observations may be mentioned a feature observed in 

 the pyramidal-tract degeneration following on destruction of the arm area 

 in the chimpanzee (v. sup., p. 192, figs. 20, 22). In the cross-section of the 

 degenerated pyramid the degenerated fibres are somewhat less numerous 

 in the ventrolateral part than elsewhere. 



And the same cases showed that some of the fibres from arm area are 

 among the highest of the fibres which decussate to the contralateral side 

 in the pyramidal decussation. 



In another of the orangs w^e made the following observations : — After 

 the hemispheres had been systematically explored with the electrode, and 



