THE MOTOR AREAS 



637 



outang, and those of Sherrington and Greenbaum on the orang-outang, gorilla 

 and the chimpanzee., are of very great interest partly because these anthropoid 

 apes stand closest in the scale to man himself,, and partly for the special 

 reason that a further progressive development of this zone from the monkeys 

 to the highest apes is therein unmistakably demonstrated. The fact of this 

 development teaches us in the clearest possible manner how careful we must 

 be in applying the results obtained from other animals to man himself. 



The general division of the motor zone as it has been made out in the 

 monkeys is the same in its larger features for the apes. There are however 



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Arrangement of excitable fibers in the internal capsule. 

 FIG. 287. Motor cortical areas in the monkey (Macacus sinicus), after Beevor and Horsley. 



several very noteworthy differences between the two groups. In the monkeys 

 (cf. Fig. 285) we find on the convex surfaces, both on the central and the 

 frontal convolutions, single excitable regions from which several kinds of 

 movements can be discharged. In the apes (cf. Fig. 288) the region on the 

 frontal convolutions contains but one field from which only movements of 

 the eyes can be induced. The posterior central convolution is entirely or in 

 very large part inexcitable, the motor cortical areas being for the most part 

 gathered together in the anterior central convolution. Again, whereas in the 

 monkeys there are no sharp demarcations between the cortical areas for 

 different groups of muscles, in the orang-outang the cortical areas for the 

 main divisions of the body are separated by regions which are inexcitable. 



