From The Wistar Institute of Anatomy and Biology, Philadelphia. 
STUDIES ON THE VARIATION AND CORRELATION OF 
SKULL MEASUREMENTS IN BOTH SEXES OF MATURE 
ALBINO RATS (MUS NORVEGICUS VAR. ALBUS). 
BY 
SHINKISHI HATAI, Pu. D., 
Associate in Neurology at The Wistar Institute. 
WITH 1 FIGURE AND 10 TABLES. 
The present investigation was undertaken to determine the size of the 
skull and the relative development of its constituent parts in the adult 
albino rat. To this end the biometric method was employed with the 
idea that in this way it would be possible to obtain more precise results 
and also with the idea of later comparing these skulls with those of the 
hybrids between Mus norvegicus and Mus rattus. 
MATERIALS AND MrtTHops oF MEASUREMENT. 
For the present study 53 male and 51 female skulls of mature rats 
(rats more than 150 days old) were measured. The following measure- 
ments were made with vernier calipers: (1) the length of the entire 
skull; (2) the fronto-occipital length; (3) the zygomatic width; (4) 
the length of the nasal bone; (5) the height of the skull; (6) the width 
of the cranium or the squamosal distance. In every case the maximum 
length alone was recorded. 
In the present paper the horizontal straight line joining the tip of 
the nasal bone to the end of the occipital bone is called the length of 
the entire skull. This however is not exactly equal to the sum of the 
length of the nasal bone and that of the fronto-occipital. 
The fronto-occipital length was determined in the following way: 
Since the length measured with the calipers from the tip of the nose to 
the posterior end of the inter-parietal bone is not always equal to the 
length measured from the tip of the nose to the end of the occipital bone, 
both measurements were taken (See Fig. 1).° The latter measurement 
is usually the longer. The difference between the two measurements was 
added to the length from the tip of the frontal bone to the end of the 
inter-parietal bone, and the sum was called the fronto-occipital length. 
AMERICAN JOURNAL OF ANATOMY.—YVOL. VII. 
9 
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