THE DEVELOPMENT OF CER'iAIN FEATURES OF THE CEREBELLUM. 



373 



In the case of hemiatrophy, the only point of interest is that we have in the 

 vermis and right hemisphere a very marked hypertrophy secondary to the atrophy 

 in the left hemisphere and also to an extent in the flocculus of both sides. 



OUTER NUCLEAR LAYER. 



The most prominent feature of figure 1 is the transitory outer nuclear layer, 

 which at this stage of development (sixth month of fetal life) occupies a most 

 superficial position in the molecular 

 layer. This outer molecular layer has 

 recently been studied in Obersteiner's 

 laboratory by Biach, and also by Lowy. 

 Biach studied the time of disappearance 

 of the layer in the human brain, and 

 found a gradual decrease in the number 

 of layers of cells until the whole dis- 

 appeared, about the eleventh month. 

 Lowy's study is comparative. He di- 

 rects attention to the disappearance of 

 the outer nuclear layer in different ani- 

 mals at very different periods, corre- 

 sponding to the ages at which myelinization in the cerebellum becomes pro- 

 nounced and locomotion is acquired. He gives a very satisfactory review of the 

 various opinions which have been advanced as to what becomes of this outer 

 nuclear layer, whether it goes to help form the inner nuclear layer or the Purkinje 



FIG. 4. Cross-section of the cerebellum of an embryo of 6 

 months, from the cortex of which figure 1 13 drawn. 



Flo. 5. Two drawings have been superimposed for convenience of comparison. The outline drawing is from 

 a fetus of 7 months, while the heavy, continuous line drawing is of a Hi-day-old child. Figures 5 and 

 6 show the tremendous increase in cerebellar cortex at the time the outer nuclear layer is disappearing. 



