PLATE 2 
EXPLANATION OF FIGURES 
12 Dorsal view of a normal untreated brain of an adult rat. 
13 Dorsal view of the brain of an adult rat showing the marked develop- 
mental arrest in the formation of the neopallium. The meninges on the left 
side of the brain are removed. Mother treated with gamma-ray irradiation on 
February 21, 1920, young were born on February 28rd. Brain from radiated 
young removed on December 31, 1920. Dose = 1350 me.hrs. (For further ref- 
erence see text.) The magnification is the same as for the drawing of the normal 
brain. 
14 A lateral view of the brain shown in figure 13. This shows the thin- 
ness of the remains of the cerebral cortex and its total absence in the frontal and 
occipital regions. (For further reference see text. ) 
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