112 E. LINDON MELLUS 



of the migrating neuroblasts are surrounded by closely packed 

 nuclei. This is quite suggestive of the way in which small objects 

 floating down stream collect temporarily about an obstruction. 

 This was not observed in the eight months brain and is possibly 

 pathological, as all the blood vessels in the new-born brain were 

 engorged. 



Thus it appears that in man, even at the period of birth, all 

 the constituent parts of the cerebral cortex are not only not in 

 situ but that the birth of new units is still going actively on and that 

 these elements are still moving from their place of origin in the 

 ventricular wall to their ultimate destination in that latest and 

 highest development of the animal organism. The latest authori- 

 tative statement as to the development of the human cerebral 

 cortex based upon personal investigation is to be found in the last 

 work of His published in 1904.^ He says the germinal cells pro- 

 duce both neuroblasts and glia cells, but he also states that here 

 and there we find developing elements where no germinal cells 

 are present and he agrees with Shaper that they must there 

 develop from undifferentiated cells. He also says the more 

 crowded they become the more both neuroblasts and spongio- 

 blasts assume the drawn out form (pear-shaped) and they can 

 only be differentiated by the visible connection of the spongio- 

 blasts with connective tissue, and the neuroblasts by the connec- 

 tion with a nerve fiber. 



Essick^ in a recent paper on the development of the pontine 

 and arcuate nuclei describes the migration of cells from the roof 

 of the fourth ventricle and the wall of the lateral recess, passing 

 through the intervening tissues in closely packed streams. This 

 behavior of the new elements seems to closely resemble that ob- 

 served in the sUdes obtained from the two brains described in 

 this paper. In the case of the developing cortex, however, the 

 closely packed cells streaming from the matrix maintained this 

 pecuhar formation only as far as the 'Ubergangschicht' and 

 from here to the cortex the migration was continued in what might 

 be called 'single file,' but it was apparently more direct. 



1 Die Entwickelung des menschlichen Gehirns wahrendes ersten Monats. Wil- 

 helm His. Lcipsig, 1904. 



2 Amer. Jour. Anat., vol. 13, p. 25. 



