330 The American Naturalist. [ April, 
the symphysis with the inferior border of the horizontal ramus, 
is less than a right angle in man, and much more than a right 
angle in the anthropoids. According to Topinard, this angle in 
fifteen Parisians is 71°.4; in fifteen African Negroes, 82°.2; in 
fifteen Neocaledonians, $3°.9; in the jaw of Naulette, 94°. In 
the best preserved jaw of Spy, the angle-is 107°, if measured 
from the inferior symphysial border, or 90° if measured from 
the inferior border of the ramus. There is no chin in the jaw 
of the Cannstadt race, and the large angle approaches without 
nearly equaling that of the anthropoids. But the posterior 
face of the symphysis presents the most remarkable peculiarity. 
In the symphysis of the apes (Figs. 3, 4,5) the posterior border 
is a continuous slope from the alveolar border to the inferior 
K 
Fic. 5. Fic. 6. Fic. 7. 
Vertical sections of symphysis mandibuli of chimpanzee (Fig. 5) ; of Spy man No. 
1 (Fig. 6), and Spy man No. 2. ( Fig. 7). From Fraipont and Lohest. 
margin, interrupted by a slight concavity below the middle. 
In the human jaw this line slopes backward to near the middle, 
where are situated the small tuberosities for the insertion of the 
genio-glossal muscles. (B in the accompanying figures.) The 
surface then slopes rapidly forward to pass into the narrow 
inferior border of the chin (Figs. 8, 9). In the jaws Naulette 
and Spy, the structure is exactly intermediate between the two, 
and quite different from both. It commences above with a 2 
posterior slope similar to that of the apes, exhibiting what is 
called by Topinard, internal prognathism, as it appears in the 
lower human races. The surface then descends abruptly, form- 
