424 Variation and Correlation of Skull Measurements 
The width of the cranium (squamosal distance) was determined by 
taking the maximum distance between the two points (right and left) 
where the zygomatic bones rest on the lateral walls of the cranium. The 
height of the skull was determined by measuring a perpendicular distance 
between the greatest convexity of the parietal bone in the median line and 
the junction line between the basi-occipital and the basi-sphenoidal bones 
on the ventral surface. 
The cranial capacity was determined in the following way: The skull 
was held vertically, with the nose downwards and was filled with fine 
shot (No. 11) to the upper level of foramen magnum and then the nose 
of the skull gently struck twice against the palm of the hand. The space 
SQUAMOSAL DISTANCE, 
FRONTO-OCCIPITAL LENGTH. 
Fic. 1. Diagram of the skull of the adult albino rat, seen from above. 
thus formed was again filled. Although this is a simple procedure yet it 
needs the greatest care and much practice in order to produce uniform 
results. The slightest variation will easily cause differences of more than 
one gram in the weight of the shot. The greater the experience of the 
observer the more uniform are the results. By practice the author has 
been able to reduce the difference between the first and second filling to 
less than one decigram in eight cases out of ten. The distribution of the 
errors in this work was found to follow the Gaussian normal curve and 
therefore it is inferred that the number of minus errors is the same as the 
number of plus errors. As a matter of fact the average difference between 
the first and second fillings did not exceed one per cent. The cranial 
capacity thus determined was finally transformed into cubic centimeters 
of brain substance (see page 435). 
