GROWTH OF THE CEREBRAL CORTEX ny. 
IV. OBSERVED DATA GIVEN IN TABLE AND CHART 
As in the ease of the albino rat, the measurement of the corti- 
cal thickness of the Norway brain was made at the localities 
I-XIII by the direct measurement of the sections as prepared 
and was then recorded without correction. The results thus ob- 
tained are condensed in table 3. 
Table 3 shows for each brain weight group the average 
thickness of the cerebral cortex of the Norway rat as directly 
observed in each of the three sections and the general average 
obtained by averaging the thicknesses of the sagittal, frontal and 
horizontal sections. The average brain weight corresponding to 
the average thickness of the cortex is obtained by doubling the 
weight of the brain, from which the sagittal and frontal sections 
were taken, adding the weight of the brain from which the hori- 
zontal sections were taken, and dividing the sum by three. 
Chart 1 is based on table 3 and shows the increase in the gen- 
eral average thickness of the cerebral cortex of the Norway rat, 
TABLE 3 
Showing the general average thickness of the cerebral cortex of the Norway rat ac- 
cording to brain weight groups, also the average thickness in the sagittal, frontal 
and horizontal sections. Observations on slide, without correction 
ates SAGITTAL SECTION ania. HORIZONTAL SECTION Renee 
WEIGHT 
GrOuE Number| Brain Thick- | Thick- | Number} Brain Thick- Brain Thick- 
of cases | weight ness ness of cases | weight ness weight ness 
grams mm. mm. grams mm. grams mm. 
N XI 3 1.164 | 1.34 1.48 3 1.164 1.44 | 1.164 1.40 
N XII 0 0 
N XIII 1 1.369 1.35 1.50 1 1.343 1.50 | 1.360 1.45 
N XIV 6 1.4380 1.43 1.48 5 1.447 1.54 | 1.486 1.48 
N XV 2 1.537 1.40 1.50 2 1-520 1.58 | 1 o32 1.49 
N XVI 8} 1.629 1.41 1.54 4- | 1.663 1.63 | 1.640 1.538 
N XVII 4 1.739 1.51 1.56 4 1.747 1.59 | 1.742 1.55 
N XVIII 2 1.829 1.51 1.64 2 1.843 1.63 | 1.834 1.59 
N XIX 2 1.972 1256 1.58 1 1.953 1.68 | 1.965 1.61 
N XX 2 2.052 1.49 1.48 2 2.018 1.58 | 2.041 1.52 
N XXI 2 242 1.53 1 533 2 2.156 75) | 2E1166 1.60 
N XXII 0 0 
N XXIII 1 2.345 1.60 1 2.345 Ste) || Bees USE 
THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 29, No. 1 
