CURVE or SPEE IN MAMMALS 
189 
the degree of the curvature of the curve of Spee, and the gnathic 
index, which is taken to represent the degree of prognathy, neither 
within a species nor within an order. To illustrate these points the 
data in tables 23 and 24 were arranged according to the diminishing 
value of the gnathic index in orang utan and in the primates. The 
data in these tables show that the value of the "center angle" and 
the degree of curvature of the curve of Spee are independent of the 
size of the teeth or the size of the skull, or the degree of prognathy. 
Relation between the "center angle" of the curve of Spee and the angle 
of the line of articulation to the hasio-nasal line 
We notice, from the data in table 17, that the average measure- 
ments given in the primates show a reciprocal relation between the 
value of the "center angle" of the curve of Spee and of the articular 
basio-nasal angle (the angle between the line of articulation and the 
basio-nasal line), if the data for man be omitted, i.e., the greater 
the "center angle" of the curve, the smaller will be the articular 
basio-nasal angle, or vice-versa. On the other hand, the average 
data for artiodactyla (table 18) show no such relation between these 
two measurements. Curiously enough, when similar data obtained 
from the different individuals of each species are compared, we do 
not find a reciprocal relation such as has just been described (see 
tables 2 to 16). This is true even when the different individuals 
compared are all of species of primates. Unfortunately, I possess very 
limited data for the other orders of mammals, and thus I am unable 
to determine whether or not there is, in other orders, a relation simi- 
lar to that shown among the primates named in table 17. 
If all available individual skulls belonging to the same species with- 
in the primates be examined, it will be seen that both the auditory 
meatus and basion (anterior border of occipital foramen) lie exactly 
or nearly on the same transverse diameter. As the fossa is always 
situated close to the auditory meatus, it is evident that the former 
has also a fixed relation to the basion in respect to the line of artic- 
ulation. Since the curve of Spee touches the anterior face of the 
articular surface of the condyle by its backward extension, it follows 
that the "center angle" of the curve must be greater if the fossa lies 
