THE STUDY OF MAN. 311 



study of its development shows that the convolutioning of the 

 cerebral hemisphere is primarily due to the connection, and differ- 

 ent rate of growth, of the superficial layer of cells with the under- 

 lying layers of white nerve fibers ; and that so far from the shape 

 being seriously modified by the constraining influence of the 

 surrounding embryonic skull, the form of the soft membranous 

 brain-case is primarily molded upon the brain within it, whose 

 shape it may however be, to some extent, a secondary agent in 

 modifying in later growth. We have also learned that, although 

 in another sense from that of the crude phrenology of Aristotle, 

 Porta, or Gall, the cerebrum is not a single organ acting as a 

 functional unit, but consists of parts, each of which has its specific 

 province ; that the increase in the number of cells in any area is 

 correlated with an increase in the size and complexity of pattern 

 of the convolutions of that area ; and that this in turn influences 

 the shape of the inclosing shell of membrane and subsequently of 

 bone. 



The anatomist and the physiologist have worked hand in hand 

 in the delimitation of these several functional areas, and pathology 

 and surgery have confirmed what experimental physiology has 

 taught. The topography of each part of the cerebrum, so im- 

 portant to the operating surgeon, should be pressed into the serv- 

 ice of the anthropologist, whose measurements of the brain-case 

 should have definite relation to these several areas. In the dis- 

 cussion which is to take place on this subject, I hope that some 

 such relationships will be taken account of. This is not the place 

 to work out in detail how this may be done ; I only desire to em- 

 phasize the fundamental principle of the method. 



The second factor which determines the shape of the individual 

 skull is the size of the teeth. That these differ among different 

 races is a matter of common observation ; thus the average area 

 of the crowns of the upper-jaw teeth in the male Australian is 

 1,536 sq. mm., while in the average Englishman it is only 1,286 sq. 

 mm., less than 84 per cent of that size.* 



It is easy to understand how natural selection will tend to in- 

 crease the size of the teeth among those races whose modes of 

 feeding are not aided by the cook or the cutler ; and how, on the 

 other hand, the progress of civilized habits, assisted by the craft 

 of the dentist, interferes with the action of selection in this matter 

 among the more cultured races. 



For larger teeth a more extensive alveolar arch of implanta- 

 tion is necessary ; and as the two jaws are commensurately devel- 

 oped, the lower jaw of the macrodontal races exceeds that of the 



* These and the succeeding averages are from my own measurements, taken from never 

 less than ten individual cases. 



