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MASARU NAGAO 
cusp of the most posterior molar. Instead of projecting the positions 
of each buccal cusp of the bicuspids and molars perpendicularly on 
this plane, I have measured the distances between each successive 
cusp and also the height of each cusp from the horizontal plane (on 
which the lower jaw rests). These two sets of measurements were 
plotted, taking the former for the abcissae and the latter for the 
ordinates. The desired curve was finally obtained by connecting the 
tips of the ordinates as shown in figure 2. This method of selecting 
the projection plane has some advantage when compared with that 
X 
.o 
Fig. 2. Showing the Projection Points of Each Buccal Cusp and the Middle 
Point of the Condyle in the Case of the Orang Utan 
Specimen 2170, right. OX, ordinate; OF, abcissa. 
of Spee, because the relative positions of the cusps of the teeth are 
better represented than when they are projected on the sagittal plane. 
My method, however, is not entirely beyond criticism owing to the 
slight curvature of the dental arch, although the curvature of the 
dental arch at the region of the bicuspids and molars is insignificant, 
amounting to not more than 3 to 4 mm. between the arch and its 
chord, in the case of the human skull. Moreover, in skulls of some 
other mammals, e.g., the orang utan and the peccary, this curvature 
is practically zero. The method adopted by me does not distort the 
