924 THE CENTRAL NERVOUS SYSTEM 



and parietal lobes on the left side. The character of the animal, 

 which had been studied for months before the operations, was en- 

 tirely unaffected. All its traits remained unaltered. There was no 

 loss of memory or intelligence. On the other hand, disturbances 

 of movement on the right side were very noticeable up till its death. 

 It learned again to use the right limbs in locomotion; but, although 

 they were not markedly weaker than those of the left side, their 

 movements had a certain clumsiness, which was associated with a 

 permanent diminution in the sensibility of the skin of these limbs. 

 Muscular sensibility was also lessened. In acts requiring the use only 

 of one hand, the right was never willingly employed, and it evidently 

 cost the animal a great effort to use it in such movements, but by 

 special training it learnt again to give the right hand when asked 

 for it, and to make use of it for other purposes. The movements 

 with which the ' motor ' areas are concerned are essentially skilled 

 movements, and we may suppose that it is more difficult for a 

 monkey to educate again a centre for such complex and elaborate 

 manoeuvres as are performed by fts hand than for a dog to regain 

 normal control of the comparatively simple movements of its paw. 

 In man in cases of hemiplegia, when the patient lives for some time, 

 a certain amount of recovery usually takes place, especially in young 

 persons, in the paralyzed leg, but much less in the paralyzed arm. 



In the lower monkeys the ' motor ' area was formerly stated to 

 extend behind the sulcus centralis into what in man would be called 

 the ascending parietal convolution (post-central gyrus), and also to 

 be more extensively represented on the mesial surface of the hemi- 

 sphere than in the higher apes. Such observations, however, require 

 to be reinterpreted in view of the results of Sherrington and Griin- 

 baum, especially as they were carried out by the bipolar method of 

 stimulation, with both electrodes on the cortex. This method does 

 not admit of such strict localization of the stimulus as the unipolai 

 method. The most recent work with the unipolar method has 

 indicated that in the lower apes also excitation of the gyrus post- 

 centralis does not cause movements (C. and O. Vogt). 



It is in the light of the results obtained in monkeys, and by the 

 aid of histological, embryological, clinical, and pathological ob- 

 servations, that the ' motor ' areas in man have to a great extent 

 been mapped out. 



The histological differentiation of the various cortical regions recently 

 demonstrated by Brodmann and by Campbell are of especial interest 

 (Figs. 372-376). It has long been customary to divide the cortex into 

 layers, although the number and the boundaries of these layers are 

 somewhat arbitrarily fixed. Brodmann distinguishes six layers: (i) A 

 zonal or peripheral layer, containing many nerve-fibres and neuroglia 

 cells, but few nerve-cells; (2) a layer containing ' granules ' and small 

 pyramidal cells (external granular layer] ; (3) a layer of medium and 

 large pyramidal cells (pyramidal layer); (4) a layer of small irregular 



