TRANSACTIONS OF SECTION H. 783 



the centre for speecb. In man certain of these have undoubtedly undergone 

 marked expansion. The skilled movements of the hands, as shown in the use of 

 tools, in writing, and so on, have not been acquired without an increase in the 

 brain mechanism by which these are guided. So important, indeed, is the part 

 played by the human hand as an agent of the mind, and so perfectly is it adjusted 

 with reference to this office, that there are many who think that the first great 

 start which man obtained on the path which has led to his higher development 

 was given by the setting of the upper limb free i'rom the duty of acting as an 

 organ of support and locomotion. It is an old saying ' that man is the wisest of 

 animals because of his hands.' Without endorsing to its full extent this view, I 

 think that it cannot be a matter for surjirise that the district of the cerebral 

 cortex in man in which the arm-centres reside shows a manifest increase in its extent. 



In the same region of cerebral cortex, but at a lower level, there are also situated 

 the centres AS'hich are responsible for facial expression. In the ape there is a con- 

 siderable degree of facial play ; but this is chiefly confined to the region of the 

 lips ; and the muscles of the face, although present in greater mass, show com- 

 paratively little of the differentiation which is characteristic of the lighter and 

 more feeble muscles in the face of man. And then as to the effect produced : These 

 human muscles are capable of reflecting every fleeting emotion, every change of 

 mind, and by the lines and furrows their constant use indelibly fix on the counte- 

 nance the character and disposition of an individual can to some extent be read. 

 As the power of C()mmunicatiou between primitive men became gradually esta- 

 blished, facial movements Were no doubt largely used, not only for the purpose of 

 giving expression to simple emotions, such as anger or jo}', hut also for giving point 

 and force to the liiltering speech of our early progenitors by reflecting other con- 

 ditions of mind. The acquisition of this power as well as the higher and more 

 varied powers of vocalisation must necessarily have been accompanied by an 

 increase of cerebral cortex in the region under consideration. And in this connec- 

 tion it is a point WfU worthy of note that the area of cortex mapped out m the 

 human brain' as controlling the muscles of the face, mouth, and throat is as large, 

 if not larger than that allotted to the arm and hand,- and yet it is questionable if 

 all the muscles under the sway of the former woidd weigh as much as one of the 

 larger muscles (say the triceps) of the arm. This is sutficient to show that it is 

 not muscle power which determines the extent of the motor areas in the cerebral 

 cortex. It is the degree of refinement in the movements required, as well as the 

 degree of variety in muscle combinations, which apparently determines the amount 

 of ground covered by a motor centre. 



Still, the increase in the amount of cerebral cortex in man due to the greater 

 refinement of movement acquired by diflerent groups of muscles is relatively 

 small ill comparison with the increase which has occurred in other regions from 

 which no motor fibres are sent out, and which therefore have no direct connec- 

 tion with muscles. 



The remarkable conclusions arrived at by Flechsig, although not confirmed 

 and accepted in all their details, have tended greatly to clear up much that was 

 obscure in the relations of the diflerent districts of cerebral cortex. More particu- 

 larly has he been able to apportion out more accurately the diflerent values to be 

 attached to the several areas of the cerebral surface. He has shown that fully two 

 thirds of the cortex in the human brain constitute what he terms ' association 

 centres.' Within these the higher intellectual manifestations of the brain have 

 their origin, and judgment and memory have their seat. They are therefore to 

 be regarded as the psychic centres of the cerebral cortex. 



' See diagram in Schiifer's article on the ' Cerebral Cortex ' in his recent work on 

 physiolog3'. 



- The comparison only refers to surface area, and this is not an absolutely true 

 criterion of the relative amount of cortex in each region. The arm-centre has a large 

 amount of cortex stowed away within the fissure of Rolando in the shape of inter- 

 locking gyri which is not taken into account in a measurement confined to the sujjer- 

 ficial surface area. Still, this does not to any great degree detract from the argu 

 meet ■^'hich follows, seeing that the discrepancy is still sufficiently marked. 



