300 Proceedings of Royal Society of Edinburgh. [sess. 
angles. If the frontal arc were relatively of the same length in 
all skulls, the point of intersection of the base line would move 
forwards and backwards as the frontal bone becomes elevated and 
depressed. This is the principle on which Schwalbe proceeds, but 
the results of the method are very unreliable. There are two 
sources of error : ( a ) as everyone knows, the relative length of the 
frontal part of the longitudinal arc is a variable quantity in 
different races, and even in different individuals of the same race ; 
(b) and further, increase in degree of verticality of the frontal 
Fig. 2. — Aberdeen Cranium. Tracing of mesial longitudinal arc obtained by 
the American periglyph. Reduced by one-half. 
region does not depend so much on the erection of the whole frontal 
bone as on an increase on its degree of curvature. 
An index of frontal inclination formed on data ascertained by 
this method may be obtained as follows : — 
Part of base line in front of perpendicular from bregma x 100 
Length of base line 
(2) A second method consists in drawing a straight line from 
the most prominent part of the glabella (i.e. anterior end of the 
base line) to the most prominent part of the frontal curve, and 
measuring the angle formed by it and the base line. 
