24 NAOKI SUGITA 
TABLE 6—Concluded 
THICKNESS OF THE CORTEX 
COE ESE: (HORIZONTAL SECTION) 
BRAIN WEIGHT | BRAIN = 
GROUP WEIGHT iam. : 
W.Bon a Loc. Loc. Loe. Loc. Loe. z 
fresh a IX X XI Ki jek oe 
Bran Ones ide 
gra ms mm. mm. mm. mm. mm, mm. mm. mm. 
INPXCEXG C1953) 155655| 11S 70s oa 2a 2S 20 de Sieiezeos 
1.958 1.34 SLs Old) emilee 2.01 | 1.81 | 2.26 
N XX e | 2.008 |} 15.55 | 11.90 | 3.10 
2228 | 2209 | ASST 3) A cb2 5 2.7 
b | 2.028 |. 15.85 | 12-00). 2:78 | 2:05.) L907 ebs715) ae 09 
2.018 1.31 2.94) 2.17 | 2.038 | °1.79 | 1.48 | 2.08 
NXT £ | 22150) 16.55 | 12:10.) 3.30 | 266.) 2.22.) 1:94) box | e2eee 
J |) 2.162). 16.25.) 12-40 | 3-60) 2es87|- 2° 1.98 | 1.57 | 2.34 
2.156 1.34 8.45 | 2.52) 2.19 | 1.96 | 1.67 | 2.34 
N XXII 
N XX a} 2.345 | 16.55 | 12:90 | 3.14) 2:58°| 2g) 2695 s4 | 2-22 
2.345 1.28 3.14] 2.58 | 2.17 | 1.69 | 1.54 | 2.22 
ence in cortical thickness is recognizable when the brain weights 
are similar. 
In the sagittal sections, the cortex attains nearly its full thick- 
ness when the brain weighs 1.63 grams (Group N X V1), while in 
the frontal and horizontal sections, this is attained somewhat 
earlier, that is, in the brains weighing 1.53 grams (Group N XV) 
(cf. charts 3, 5, 7, 8). In the general average thickness of the 
cortex of the Norway rat, the full thickness is attained in the 
brains weighing about 1.53 grams, at which phase the body weight 
observed is about 55 grams (tables 1 and 2) (chart 8). In the 
full grown Norway rat at brain weights between 1.6 and 2.4 
grams, the average cortical thickness ranges between 1.97 and 
2.14 mm., with a mean value for Groups N XVI-N XXIII (table 
7) of 2.06 mm. The average thickness for each locality is given 
in table 8 for the Norway rat, together with the corresponding 
values for the Albino, thus making it possible to compare the 
cortical thickness in the two forms. 
