OCTOBEil 25, 1901.] 



SCIENCE. 



641 



the territory of the frontal and parietal 

 districts. This is a striking process in the 

 brain development of man, and it results 

 in a depression of the Sylvian fissure or 

 the lower frontier line of the frontal and 

 parietal lobes. Further, to judge from the 

 oblique direction of the Sylvian fissure in 

 the brain of the ape, the process is peculiar 

 to man ; in the simian brain there is no 

 corresponding increase in the area of cere- 

 bral cortex under consideration. 



I do not think that it is difficult to ac- 

 count for this important expansion of the 

 cerebral surface. In the fore part of the 

 region involved are placed the groups of 

 motor centers which control the muscular 

 movements of the more important parts of 

 the body. These occupy a broad strip of 

 the surface which stretches across the 

 w^hole depth of the district concerned. 

 Within this are the centers for the arm 

 and hand, for the face, the mouth and 

 the throat, and likewise, to some extent, 

 the center for speech. In man certain of 

 these have undoubtedly undergone marked 

 expansion. The skilled movements of the 

 hands, as shown in the use of tools, in writ- 

 ing, 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 per- 

 fectly is it adjusted with reference to this 

 oflice, that there are many who think that 

 the first great start which man obtained on 

 the path which has led to his higher devel- 

 opment was given by the setting of the 

 upper limb free from 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 sur- 

 prise that the district of the cerebral cortex 

 in man in which the arm-centers 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 

 centers which are responsible, for facial ex- 

 pression. In the ape there is a consider- 

 able 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 comparatively 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 pro- 

 duced : These human muscles are capable 

 of reflecting every fleeting emotion, every 

 change of mind, and, by the lines and fur- 

 rows their constant use indelibly fixes on the 

 countenance, the character and disposition 

 of an individual can to some extent be read. 

 As the power of communication between 

 primitive men became gradually estab- 

 lished, facial movements were no doubt 

 largely used, not only for the purpose of 

 giving expression to simple emotions, such 

 as anger or joy, but also for giving point 

 and force to the faltering 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 vocalization must neces- 

 sarily have been accompanied by an in- 

 crease of cerebral cortex in the region 

 under consideration. And in this con- 

 nection it is a point well worthy of note 

 that the area of cortex mapped out in the 

 human brain, -i^ as controlling the muscles of 

 the face, mouth and throat, is as large if 

 not larger than that allotted to the arm and 

 hand,t and yet it is questionable if all the 



*See diagram in Schiifer's article on the ' Cerebral 

 Cortex ' in his recent work on physiology. 



t 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 arra-center 

 has a large amount of cortex stowed away within the 

 fissure of Eolando, in the shape of interlocking gyri, 

 which is not taken into account in a measurement 

 confined to the superficial surface area. Still, this 

 does not to any great degree detract from the argu- 

 ment which follows, seeing that the discrepancy is 

 still sufficiently marked. 



