SUMMATION BY CHAIRMAN 



161 



ON THE 



ADULT CEReBELLUMS 

 THAT RESULT FROM 200r> 

 OM THE DAY 5HoWN 



IIttlE BRAIM5 SUOwJ 

 5rA,C>E Ar Tirf\e OF 

 RADIATION 



ON 7 He 3«o DAY 



On thc Ist 



(teSTHATAL PAV 



<:& 



Radiatiom om 



THE ZiiT FerAL DAY 



Fig. 3. The spectrum of cerebellar malformations produced by 200 r fror 

 fetal to neonatal life. (.Adapted from Hicks and D'.\mato, 1960b.) 



late 



actual brains representing the gross patterns of cerebellar malformation in the 

 albino rat that result from 200 r on the days indicated. In the gray rat, as in the 

 mouse, the cerebellum is a little more advanced in its schedule of development 

 than in the albino rat. The little brains, drawn to scale, show the fetal or neonatal 

 brain as it was when radiation was given. Malformations induced at earlier stages 

 are described by Hicks et al. (1959). In certain respects there is a front to back 

 sequence of maturation of folia and a lesser center to lateral sequence, which is 

 reflected in a corresponding sequence of deformations. To press this generality 

 further would be misleading, because difTerent regions, and even parts of folia, 

 wax and wane in their growth patterns. While the folial pattern is maturing, the 

 cytologic characteristics of the cerebellum are also being unfolded, and the cyto- 

 architectural malformations do not at all parallel the folial malformations. The 

 malformations induced in late fetal life are characterized by a normal cyto- 

 architecture, while those representing the end of the 1st week are characterized 

 by an ectopic, extra granule cell layer, outside rather than deep to the Purkinje 

 layer. Damage to the neuroepithelium, which in the developing cerebellum comes 

 to lie on its surface instead of lining a ventricle, results at this stage in a preco- 

 cious coarse growth of the Purkinje dendrites. This, we think, blocks the further 

 migration of the primitive cells which would complete the granule layer. The 

 late comers simply stop in the molecular layer. Irradiation on the first days after 



