498 NAOKI SUGITA 



values. As I measured all the material in the same manner, the 

 data thus obtained are comparable among themselves. 



I have arranged the individuals in twenty groups, numbered 

 according to the number of decigrams in the brain weight of 

 each, for example, brains weighing 0.300-0.399 grams form Group 

 III and brains weighing 1.500 to 1.599 grams Group XV, etc. 

 In each group, the individual was designated as a, or b, or c, 

 etc. in the order of the date of the dissection. Each individual 

 carries the same designation when the record for it appears in the 

 other studies in this series. Measurements of the body and 

 brain weights, body and tail lengths, were made by the usual 

 methods employed at The Wistar Institute (see ''The Rat," 

 Donaldson, '15). 



As the individual records will, for the most part, be given in a 

 study, which follows, on the growth of the cortex, and as all of 

 the records are on file at The Wistar Institute, it has not been 

 thought necessary to print them here. In table 2, the mean 

 values for each brain weight group are entered with a statement 

 of the number of individuals on which the average has been 

 based. 



In table 2 are given for comparison the standard body weight 

 and body and tail lengths and the age, corresponding to the ob- 

 served brain weights, and obtained by the use of formulas devised 

 by Hatai (see "The Rat," Donaldson, '15). Some discrepancies 

 seen in the case of Groups XVI-XX between the observed and 

 calculated values are due to the fact that in grown-up rats the 

 brain weight increases very slowly, while the body measure- 

 ments are open to wide variations. 



III. POSITIONS OF DIAMETERS 



The positions of the five diameters, by measurement of which 

 the §hape and size of an albino rat cerebrum are to be deter- 

 mined, are as follows (figs. 1 and 2). 



1. Width AB (abbreviation W. B), the greatest width along 

 the frontal plane (fig. 1). 



2. Width CD (abbreviation W. D), passing through the middle 

 point O of the fissura sagittalis and parallel to AB (fig. 1). 



