130 Proceedings of the Royal Society of Edinburgh. [Sess. 
indices based on it, and referred to later. Two of these curvature indices, 
calculated in accordance with the procedure laid down by Schwalbe (19), 
have already been published by Berry and Robertson. They were 
estimated by taking the proportion which the length of the chord bears 
to the length of the arc, the latter being taken as 100. Klaatsch (20), 
on the other hand, in his work on the Australian and other skulls, 
estimates these indices of curvature quite differently, and says : “ To 
properly appreciate a sloping forehead, the only part of practical im- 
portance is that between the glabella and bregma. The simplest way of 
determining it, though not employed so far as I am aware, is to measure 
the greatest distance of the curved surface of the frontal from the 
glabella-bregma line (i.e. the chord of frontal curvature), and to form 
an index comparing this greatest distance with the length of the glabella - 
bregma line.” 
By multiplying the length of the greatest distance of the chord from 
the arc by 100, aUd dividing by the length of the chord, he constructs his 
index of curvature for the ossa frontale, parietale, et occipitale. It will 
thus be seen that Klaatsch’s index expresses the ratio of the maximum 
distance of arc from chord to the length of the chord, the latter being 
taken as 100. 
I am not at all convinced that the above method will do all that 
Klaatsch endeavours to claim for it. It will, of course, be admitted that 
as a method of determining the amount of curvature it fulfils its purpose ; 
but, in my opinion, it fails to express the degree of the recession of the 
forehead, for, as demonstrated by Schwalbe and others, the sloping forehead 
can only be estimated by angular measurements on a suitable base-line. 
It is, therefore, extremely difficult to see how Klaatsch’s method of dealing 
with the chord of the os frontale and its distance from the arc without the 
use of any base-line whatsoever can express the recession or otherwise 
of the forehead. 
This apart, it is an excellent method of determining the degree of 
curvature of the bone, and is probably preferable to Schwalbe’s method, 
though, it may be noted, the degree of curvature of any cranial bone can 
now be estimated directly by means of Mollison’s cyclometer. 
Turner (21) and Cunningham (22) have also estimated the curvatures of 
various longitudinal osseous segments of the skull in a somewhat similar 
manner to Klaatsch, but do not construct an index of curvature. They 
simply record the greatest distance of the arc from its chord, and, in the 
case of the os frontale, prefer the nasion-bregma or total frontal arc and 
chord to the glabella-bregma measurements. 
