Literary Notices. 209 



horizontal and midway between these two, /. e., a plane making an angle ot 45° 

 with the horizontal — it is possible to obtain three pairs of measurements in each 

 hemisphere, by which the relative development of the frontal and parietal association 

 areas can be compared the one with the other, as well as with those of the other 

 hemisphere and of other brains, and can be expressed in an arbitrary numerical 

 form which lends itself to statistical treatment. 



As an example of the results obtained by the use of this method I might quote 

 some figures taken from Table I la (p. 366). In a series of 34 brains of white men 

 and 43 black men, in which the average length of Mall's axis is the same (168 mm.), 

 the average distance of the center of the left frontal area (the place where the 60° 

 radius cuts the surface in the plane 45° above the horizontal) from the center of the 

 axis is 70 mm. in the whites and only 66 mm. in the blacks, whereas the center of 

 the left parietal area (measured along the 120° radius) is 71 mm. in the whites and 

 73 mm. in the blacks. 



The time will soon come when we must attempt to estimate the exact area and 

 volume of gray matter in each different histological area of the cerebral cortex in a 

 series of brains of different races. This possibility has become opened up by the 

 discovery that in perfectly fresh human brains the difference in the color and 

 te.xture of the different cortical areas is quite recognizable by the naked eye, so 

 that each area can be cut out and by snipping away the white matter (with a scissors 

 under water) the cortex may be spread out in one plane and its exact extent esti- 

 mated. This method, however, is so exceedingly difficult and exacting that it 

 will be a long time before a large series of records can be obtained. Until this is 

 done the results obtained by the much simpler method devised by Dr. Mall will 

 provide us with information of the utmost value. 



In the absence of any absolute measurements of the extent of the cortical areas, 

 the exact size of the surface of the corpus callosum and its various parts as exposed 

 in mesial sagittal section is the surest guide to the relative development of the 

 cerebral cortex and its parts that we possess at present. It is, therefore, particularly 

 instructive to note that the separation of the races exhibited in Dr. Bean's table 

 of the relative proportions of the anterior and posterior halves of the corpus cal- 

 losum, and of its genu and splenium, is much sharper than that shown in the cruder 

 measurements of the radial distances of the frontal and parietal areas from an 

 arbitrary point. 



The results obtained by Dr. Bean in his compajison of the left and right hemi- 

 spheres (pp. sysys) ^•'^ particularly interesting, seeing that they agree with 

 the evidence yielded by other modes of investigation and give numerical expression 

 to the differences. 



The fact that a "smaller posterior association center" is found "on the left side 

 of the Caucasian" (p. 371) is a very instructive observation when it is recalled that 

 as a general rule the left occipital region is much more pithecoid than the right 

 because the visual cortex has been pushed backward toward the mesial surface 

 by the parietal expansion to a much less extent than in the other hemisphere. 



The fact that there is "a more marked racial difference on the right side than 

 on the left" (p. 372) is borne out by my own observations that in all human brains 

 the left parieto-occipital region shows a tendency toward a simpler and more ape- 

 like conformation than the right and that in negro brains there is much less asym- 

 metry in this area than there is in non-negro races. This implies a much greater 



