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MASARU NAGAO 
curve of Spec); (b) a curved line which, possessing several maxima, 
resembles an undulating curve; and (c) a type which is best repre- 
sented by a straight line. The first type may be further divided into 
two kinds; one in which, in its backward extension in the projection 
plane, the curved line touches the anterior face of the articular sur- 
face of the condyle; another, in which the curved line does not do this. 
2. The length of the radius of the circle of which the curve of Spec 
is a part was selected as a standard for comparison of the curvature 
of the arc, and the "center angle" which subtends a given length of 
the curve, was chosen as the standard in comparing the curve of Spee 
in different mammals. From the data obtained by these two kinds 
of measurements in several orders of mammals, the following results 
were calculated. 
Of the primates examined, Macacus nemestrinus has the longest 
radius (10.17 cm.), Hylobates miilleri has the shortest radius (5.50 
cm.), and man takes an intermediate position, having a radius of 
7.55 cm. Of the artiodactyla, Porcus babyrussa has the shortest 
radius (11.22 cm.), while Camelus bactrianus has not only the longest 
radius (23.99 cm.) in this order, but also the longest among all the 
mammals examined. 
In the case of the "center angle," the following relations were 
found: Among the primates, Simla satyrus has the greatest angle 
(35.6 degrees), Macacus nemestrinus the smallest (16.3 degrees), 
while man with 28.6 degrees occupies an intermediate position in 
the order. Among the artiodactyla, Porcus babyrussa has the great- 
est angle (31.3 degrees), and Lama huanacho the smallest (23.4 de- 
grees). Rhinoceros was found to possess the greatest angle (38.4 
degrees) among all the mammals examined. 
3. Neither the curvature of the curve of Spee nor the "center angle" 
of the curve increases or decreases regularly according to the zoo- 
logical order to which the animal belongs. 
4. Neither the curvature nor the magnitude of the "center angle" 
of the curve of Spee varies proportionately with the size of the teeth, 
the size of the skull, or the degree of prognathy of the skull. 
5. (a) Spec's conclusion that there is a close relation between the 
radius of the curve of Spee and the inclination of the fossa mandib- 
