684 



SCIENCE. 



[N. S. Vol. XIV. No. 357. 



ningham, of Dablin, was devoted to a 

 coasideration of the characteristics of the 

 human brain and their significance. After 

 pointing out the necessity for greater atten- 

 tion on the part of craniologists to the re- 

 lations which exist between the brain and 

 the cranium, reference was made to the 

 discussions as to the relative development 

 of the occipital lobe in man and apes, which 

 enlivened the meetings of the Association 

 forty years ago. With the knowledge we 

 now possess it seems strange that such a 

 discussion was ever precipitated, for not 

 only is the occipital lobe largely developed 

 in the ape, but it possesses even a greater 

 development than in man. Measured along 

 its medial border the percentage length of 

 the lobe to the entire length of the cere- 

 brum in the baboon, orang and man is, re- 

 spectively, 29.7, 23.2 and 21.2, and even 

 these figures do not show the full prepon- 

 derance of the occipital lobe in the ape, for 

 its anterior border extends so far forward 

 as to overlap a portion of the parietal lobe 

 and form an occipital operculum, a condi- 

 tion entirely lacking in man. Instead, 

 then, of the preponderance of the occipital 

 lobe being the distinguishing feature of 

 the human brain, it is the greater relative 

 development of the parietal, which en- 

 croaches to a certain extent upon the terri- 

 tory occupied in the lower forms by the 

 occipital. 



The conclusions of Eiidinger, derived 

 from a study of the brains of a number of 

 distinguished men, that the intellectual en- 

 dowment of an individual stands in rela- 

 tion to the development of the upper part 

 of the parietal lobe. Professor Cunningham 

 believes to be entirely without foundation. 

 Indeed, in the evolutionary development of 

 the cerebral cortex it is the lower part of 

 the lobe which shows the greater relative 

 increase and has extended itself both back- 

 wards and downwards, the latter process 

 leading to a marked depression of the Syl- 



vian fissure to an extent quite foreign to 

 the brain of any ape. And in this connec- 

 tion it is interesting to note that the recent 

 studies of the brains of the astronomer 

 Hugo G-ylden and of the mathematician 

 Sophie Kowalewsky by E-etzius, of Helm- 

 holtz, by Hansemann and of the musician 

 Eudolph Lenz by Guszman, have all re- 

 vealed an apparently marked development 

 of the cortex of the lower parietal region. 

 Furthermore, it is an interesting fact that 

 in the left cerebral hemisphere the Sylvian 

 fissure is more depressed than in the right. 

 It is well known that physiologically the 

 left hemisphere shows a decided preemi- 

 nence, to account for which various theories 

 have been suggested. That it is due to 

 the greater bulk or weight of the hemis- 

 phere seems to have been disproved, nor 

 can it be held to be due to the greater com- 

 plexity of the convolutions, nor to a better 

 blood supply. 



What, then, may have been the cause 

 both of this asymmetry and of the general 

 development of the parietal lobe. Profess- 

 or Cunningham points out that in the parie- 

 tal region are the centers for the arm, hand, 

 face, throat and mouth and, to a certain ex- 

 tent, the motor center for speech, and the 

 center for the facial muscles. These latter, 

 it is true, present a greater bulk in the ape 

 than in man, but both they and the mus- 

 cles governed by the other centers named 

 are certainly more highly dificrentiated 

 and capable of performing movements of 

 greater refinement than in the ape, and it 

 is this very degree of refinement which de- 

 termines the amount of the area covered by 

 a cortical center, rather than the mass of 

 the organ supplied. On this basis, then, 

 the greater development of the parietal lobe 

 in man is readily explained, and since it is 

 well known that the motor center for speech 

 is asymmetrical and on the left side, an ex- 

 planation is afforded of the asymmetrical 

 development of the lower parietal region in 



