TRANSACTIONS OF SECTION IT. 781 



operculum. There is not a trace of such an arrangement in the human brain, and 

 even in the anthropoid ape the opei'cuhim has become greatly reduced. Indeed, 

 in man there is e.xactly the reverse condition. The great size of the parietal lobe 

 is a leading human character, and it has partly gained its predominance by pushing 

 backwards so as to encroach, to some extent, upon the territory which formerly 

 belonged to the occipital lobe.' A great authority " on the cerebral surface 

 refers to this as a struggle between the two lobes for surface extension of 

 their respective domains. ' In the lower apes,' he says, ' the occipital lobe proves 

 the victor : it bulges over the parietal lobe as far as the first annectant gyrus. 

 Alread}-, in the orang, the occipital operculum has suffered a great reduction ; and 

 in man the victory is on the side of the parietal lobe which presses on the occipital 

 lobe and begins, on its part, to overLip it.' Now that so much information is 

 available in regard to the locahsation of function in the cerebral cortex, and 

 Flechsig has stimulated our curiosity in regard' to his great ' association areas ' in 

 which the higher intellectual powers of man are believed to reside, it is interesting 

 to speculate upon the causes which have led to the pushing back of the scientific 

 frontier between the occipital and parietal cerebral districts. 



The parietal lobe is divided into an upper and a lower part by a fissure, which 

 takes an oblique course across it. Rudinger,^ who studied the position and inclina- 

 tion of this fissure, came to the conclusion that it presents easily determined 

 differences in accordance with sex, race, and the intellectual capacity of the indi- 

 vidual. He had the opportunity of studying the brains of quite a number of 

 distinguished men, amongst whom were Bischoft" of Bonn, Dulliuger of Munich, 

 Tiedemann of Heidelberg, and Liebig of Munich, and he asserts that the higher 

 the mental endowment of an individual the greater is the relative extent of the 

 upper part of the parietal lobe. 



There is absolutely no foundation for this sweeping assertion. "When the 

 evolutionary development of the parietal part of the cerebral cortex is studied 

 exactly the reverse condition becomes manifest. It is the lower part of the 

 parietal lobe which in man, both in its early development and in its after growth, 

 exhibits the greatest relative increase. Additional interest is attached to this 

 observation by the fact that recently several independent observers have fixed upon 

 this region as one in which they believe that a marked exuberance of cortical 

 growth may be noted in people of undoubted genius. Thus Retzius has stated 

 that such was the case in the brains of the astronomer Hugo Gylden,^ and the 

 mathematician Sophie Kovalevsky ; '' Hansemann '^ has described a similar condi- 

 tion in the brain of Ilelmholtz ; and Guszraan '^ in the brain of Rudolph Lenz, the 

 musician. Some force is likewise added to this view by Flechsig, who, in a recent 

 paper,*^ has called attention to the fact that within this district there are located 

 two of his so-called ' Terminalgebiete,' or cortical areas, which attain their func- 

 tional powers at a later period than those which lie around them, and which may 

 therefore be supposed to have specially high worii to perform. 



Without in any way desiring to throvi' doubt upon the observations of these 

 authorities, I think that at the present moment it would be rash to accept, without 



' It is necessary to emphasise this point, because in Wiedersheim's fitrucinre of 

 3/cin we are told that in man there is a preponderance of the occipital lobe, and that 

 the parietal lobe is equally developed in man and anthropoids. 



- Eberstaller, }Vie7ier Medizinisclw Blatter, 1884, No. 19, p. 581. 



^ Beitrdgc inr Anatomie und Emhryoloijie, als Festgabe Jacob Henle, 1882. 



■* Ketzius, Biolo/jische Untermchiingen, neue Folge, viii. 1898, 'Das Gehirn des 

 Astronomen Hugo Gyldens.' 



^ Retzius, Biologisclie Untersucliwigen, neue Folge, ix. 1900, 'Das Gehirn der 

 Mathematikerin Sonja Kovalevsky.' 



" Hansemann, Zeitschrift fiir Psychologie und Physiologie der Slnnesorganc, 

 Band xx. Heft 1, 1899, ' Ueber das Gehirn von Hermann v. Helmholtz.' 



' Josef Guszman, Anatomischer Anzeiger, Band xix. Nos. 9 and 10, April 1901, 

 ' Beitrilge zur Morphologic der Gehirnoberflache.' 



*• Flechsig, ' Neue Untersuchungen iiber die Markbildung in den menschlichen 

 Grosshirnlappen,' Neurologisclies Centralblatt, No. 21, 189S. 



