168 
MASARU NAGAO 
The position of K was determined by the following method. Since 
the distance between the points K and i had been already determined, 
as well as the vertical distance of the point K from the base-Une, the 
position of K corresponds to the point of intersection made by the 
arc drawn by the radius iK (the point i being taken as the center of 
the arc) and by the vertical height of K along the abcissal line. Final- 
ly a curve was drawn passing through as many of the points as possible 
in order to determine whether or not the curve thus obtained is a 
circle. If the curve was a circle, the second question was whether 
or not this circle would pass through (or nearly through) the point K. 
The foregoing method cannot be appUed to the jaw of the muskrat 
on account of the difficulty in making the measurements on a speci- 
men of such small size (nasion-basion diameter about 4 cm., the total 
length of the teeth^ about 1.5 cm.). Therefore I made use of the 
following device: a small piece of paper (2.5 cm. by 1.0 cm.) was 
placed against the lateral side of the teeth and was rubbed with a 
pencil in order to trace the positions of the buccal cusps of the teeth. 
The positions of the cusps thus obtained were transferred to another 
sheet of paper by piercing these points with a needle. In order to 
determine the position of the point K, first the distance between the 
disto-buccal cusp of the first bicuspid and point K (on the plane of 
projection), and the distance between the disto-buccal cusp of the 
most posterior molar and point K, were determined. The point of 
intersection made by the two arcs, drawn with these two measure- 
ments as radii and the two corresponding points (first bicuspid and 
the most posterior molar) as the centers, is the desired point K. 
Results of the examination 
All the skulls I have examined may be arranged in four groups 
according to the form of the curve which was obtained by connecting 
the summits of the buccal cusps of the bicuspids and molars. 
1. The group of skulls, in which the curved Hne corresponds to the 
arc of a circle, and touches at the same time the anterior face of the 
articular surface of the condyle or K. To this group belong man, 
' The total length of the teeth means the distance from the mesial aspect of the first 
bicuspid to the distal aspect of the most posterior molar, all in situ. 
