STUDY OF BRAINS OF SIX EMINENT SCIENTISTS AND SCHOLARS. 227 



related ape. We find expression for these differences not only in the degree of fissural 

 and gyral development of the cerebrum, but also in the actual weight of the brain- 

 The range of brain-weight within the human species is a very wide one, from a 

 TurgenefF's brain weighing 2012 grams or a Cuvier's weighing 1830 grams to that of 

 a Zulu weighing only 1050 grams. There is a distinct gap between the lowest brain- 

 weight of a normal human being and the highest figure recorded for an anthropoid 

 (-425 grams in a gorilla), but more finds of a pithecanthropoid character like that 

 found in the Trinil bed in Java will speedil}^ serve to supply the deficiency. 



The pattern of the fissures and convolutions in the brains of the higher anthro- 

 poids and man presents the same general features in all these types. As we trace the 

 stages of the development of man's great brain through the lower forms we observe 

 how, in a number of ways, in consequence of the demands of evolution, certain regions 

 of the cerebrum assume a greater energy of growth and expand in proportion to the 

 rise in functional dignity of these areas. These regions of " unstable equilibrium " 

 present numerous details of fissural and gyral arrangement which differ not only in 

 different individuals but also in the cerebral halves of the same individual. The care- 

 ful study of these regional redundancies has resulted in the formulation of a most im- 

 portant statement in the physiology of the central nervous system. Man and the 

 higher anthropoids possess many points in common with reference to their anatomic 

 structure, their habits and their mode of life ; but over and above these traits man 

 possesses an associative memory or ability to register and compare sensations far 

 greater than that of the highest ape. Small wonder, then, that this supremacy of the 

 intellect should find somatic expression in the greater size and complexity of structure 

 of the human brain. That is why the association areas constitute the greater portion 

 of the cerebral cortex of man's brain. This relative increase of association-cortex de- 

 mands a still more intricate inter-connection of the many nerve cells by a multitude 

 of association fibers ; hence the great preponderance of white matter in the brain of 

 man as compared with that of any inferior species. These coordinating fibers never 

 project outward from the brain to the periphery. They are as truly representative of 

 the complexity of man's thought-apparatus as the number of inter-connecting wires 

 within a telephone " central " station is indicative of the amplitude of connections 

 possible in that system. A brain made up of gray matter only would be as useless as 

 a telephone system with all its inter-connecting wires destroyed. 



With the aid of the microscope the maturing of the brain-elements can be fol- 

 lowed from the earliest stages of embryonic life to the period of senescence. One of the 

 important stages in the growth of each nerve-element within the brain is the acquisi- 

 tion of a medullary sheath which surrounds the axis-cylinder process (axone) along 



