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MASARU NAGAO 
higher in the skull; and similarly, when the "center angle" is small, 
the fossa must lie lower in the skull of the same size. Combining 
these facts, it is conceivable that the relation of the basion to the 
line of articulation, or the articular basio-nasal angle, is related re- 
ciprocally to the "center angle" of the curve of Spee. Whether or 
not this explanation holds true for the skulls of different sizes cannot 
be definitely decided until more data are obtained, though it is my 
firm belief that such a relation is probable. 
I stated before that the relation between the value of the "center 
angle" of the curve of Spee and of the articular basio-nasal angle is 
reciprocal, when different species of primates, with the exception of 
man, are arranged in series. In man the "center angle" is as large 
as 28.6 degrees and occupies the second position in the table, while 
the articular basio-nasal angle is not correspondingly smaller (36.8 
degrees), but holds the sixth position (table 17). For the exceptional 
relation in man when compared with other primates, the following 
explanation seems plausible. 
If a human skull is compared with the skulls of some other species 
d.mong the primates, for example with the skull of an orang utan, 
it will be noted that the relative position of the auditory meatus and 
of the fossa is remarkably different; namely, when the line of artic- 
ulation in both skulls is fixed parallel to the same horizontal plane, 
the auditory meatus of the human skull occupies a position slightly 
below the fossa, while on the contrary in the orang utan, it occupies 
a position slightly above it. This difference in the position of the 
auditory meatus and the fossa in the two species may be related to 
the factors which we now wish to discuss. If the skull of the orang 
utan is compared with that of man, it is evident that the latter shows 
a relatively greater development of the cranium. It therefore follows 
that in association with the greater growth of the cranial part, the 
occipital portion suffers a backward and downward extension, and 
as a consequence both the auditory meatus and the occipital fora- 
men occupy slightly lower positions than in the orang utan. This 
difference in the relative position of the occipital foramen, and con- 
sequently of the basion, in the two forms seems to me to be a factor 
contributing to the enlargement of the articular basio-nasal angle in 
man, thus giving him an anomalous position in the table. 
