182 
MASARU NAGAO 
VI. DETERJilNATION OF THE DENTAL AND GNATHIC INDICES 
Dental index 
"The dental index is the standard of measurement of the size of the 
teeth to the dimensions of the skull, and may be ascertained by means of 
the following formula, the length of the distance being marked out by the 
help of specially contrived calipers: 
The length of the teeth X 100 
The basio-nasal line 
The length of the teeth means the distance from the mesial aspect of the 
first bicuspid to the distal aspect of the m.ost posterior molar, all in situ; 
thie basio-nasal Hne is an imaginary line drawn from a spot on the middle 
line of the anterior margin of the foramen magnum of the occipital bone 
(the basion), to the junction of the nasal bones, with the nasal process of 
the frontal bone in the center of the lower edge of the nasal notch." 
(HopeweU-Smith) . 
I have obtained the data on the dental index for the purpose of 
comparing the size of teeth of each animal, and at the same time to 
determine whether or not there exists any relation between this dental 
index and the curve of Spee. The values of the dental index thus 
obtained are given in tables 2 to 18. 
Gnathic index 
"The degree of projection of the upper jaw is expressed by the gnathic 
index, which represents the ratio of the distance between the 'basion' and 
the 'alveolar point,' to the distance between the 'basion' and the 'nasal 
point,' i.e., the point of junction of nasal an(i frontal bones on the middle 
line. Thus the gnathic index is obtained by ascertaining the value of the 
Basio-alveolar line X 100 
Basio-nasal line" 
(Hopewell-Smith) . 
My object in obtaining the gnathic index was to test the state- 
ment made by Spee that there is some anatomical relation between 
the prognathy of the jaw and the curve of Spee. The values for this 
index are given in tables 2 to 18. 
