RELATIVE WEIGHT AND VOLUME OF THE COMPONENT PARTS 



OF THE BRAIN OF THE HUMAN EMBRYO AT DIFFERENT 



STAGES OF DEVELOPMENT, 



INTRODUCTION. 



The following volumetric study of the developing encephalon in the human 

 embryo was undertaken as a supplementary part of a program of investigations 

 in the morphology and differentiation of the central nervous system with which I 

 have been engaged for several years. The work was made possible through the 

 kindness of Dr. Streeter who, in furtherance of its purpose, has placed at my 

 disposal the collection of embryos of the Carnegie Laboratory of Embryology, to- 

 gether with models, notes, and such other related material as has been accumulated. 

 Under these conditions it was possible to secure a sufficient number of develop- 

 mental stages for the investigation, including the consideration of the relative rate 

 of growth of the various parts of the encephalon during the whole period of intra- 

 uterine life. It is with pleasure that I take this opportunity to acknowledge my 

 indebtedness for the hospitality, aid, and interest that have been extended to me on 

 the part of the staff of this laboratory. 



The question of growth of the animal body as a whole and of its various com- 

 ponent parts has occupied the minds of many investigators over a long period of 

 time, and yet in the mass of literature which has resulted from these studies com- 

 paratively little is to be found that deals with the volumetric development of the 

 central nervous system in the human embryo. A study of the literature on the 

 subject of weight, size, degree of development, etc., of the brain reveals the fact 

 that practically all of the observations reported have dealt with postnatal material 

 and the great majority with adult brains, secured in the main from various institu- 

 tions, such as asylums for the insane, almshouses, and homes for the aged. The 

 great questions seem to have been those concerning body size, the attempted 

 correlations between brain size and intellectuality, and the controversy over the 

 differences in brain size in the two sexes. Not a few reports frankly deal with 

 grossly pathological material. Much additional work, of anthropological value 

 mainly, has been done along the lines of craniometry, notably by West (1894), who 

 made a number of observations upon school children of both sexes, recording the 

 head measurements as a part of the general growth conditions, Lewandowsky 

 (1910), and Hrdlicka (1919), who treat of the more pertinent question of the 

 correlation between skull size and cranial capacity. 



Aside from these latter cases the bulk of the work reported may be roughly 

 grouped into four divisions : 



(a) The study of brains of individuals of superior intellectual attainments 

 (Spitzka, 1907; Marshall, 1892; Manouvrier, 1885). 



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