208 Leyton and Sherrington 



part of the left inferior frontal gyrus in a very vociferous chimpanzee has 

 probably not much weight in regard to the possible functions of that con- 

 volution in man. The experiment and its negative result were mentioned 

 in our preliminary communication, at a date prior to the interesting and 

 important controversy as to the functions of that gyrus which has led to 

 so much recent inquiry in regard to human material. 



As regards the secondary degeneration in bulb and cord, they show that 

 the pyramidal tract in the anthropoid (chimpanzee) more closely resembles 

 the human than does that of any other animal so far examined. In the 

 chimpanzee as in man there is a well-marked uncrossed ventral column 

 bundle belonging to the tract, and as in man so in the chimpanzee, to judge 

 from our experiments, though they are few, much individual variety exists in 

 the relative size of that bundle to the rest of the tract (13). The uncrossed 

 ventral column bundle shows degeneration after arm area lesions as well as 

 after leg area lesions, but in the latter case its degeneration is traceable 

 into the lumbar region, whereas in the former it ceases much higher up 

 the cord, although there it may be large. The degeneration at the region 

 of the pyramidal decussation shows in addition to the main mass of fibres 

 crossing to the contralateral lateral column a small number of fibres sloping 

 backward towards the ipsilateral column, as has been shown for the smaller 

 monkeys (25, 41, 43), and presumably holds also for man. It is this 

 uncrossed pyramidal tract slip entering ipsilateral lateral column which 

 probably accounts for the scattered slight degeneration in the pyramidal 

 tract area of the lateral column of the cord ipsilateral with the cortical 

 lesion, an ipsilateral degeneration observed in all of our experiments. The 

 pyramidal-tract degeneration after the arm area lesions was traceable to 

 much below the brachial enlargement (cf. Sutherland Simpson and 

 W. A. Jolly (43)), but did not reach the lumbo-sacral. In the grey matter 

 of the ventral grey horn of the side contralateral to the cortical lesion a 

 heavy degeneration in the minute fibres was evident, in the brachial 

 segments after arm area lesion, in the lumbo-sacral enlargement after leg 

 area lesion. 



IV, Experiments on Gyrus centralis posterior. 



Our experiments on this portion of the cortex may be divided into two. 

 groups : — 



1. Observations by stimulation. 



2. Observations by ablation. 



1. Results of Stimulation. 



Faradism, applied to the free face of centralis posterior in the same manner 

 as to gyrus centralis anterior, although readily evoking motor responses from 

 the latter, failed to excite in a similar way any detected motor responses 

 from gyrus centralis posterior in chimpanzee, orang, or gorilla. In all our 

 experiments this experiment was made, and in all the same negative result 



