158 THE STRUCTURE OF MAN 
of the first series, are as a rule far less modified than the 
permanent teeth; and since, in view of this, it is found that 
the former agree in Anthropoids and Man far more than the 
latter, we are justified in concluding that the teeth of both 
Man and the Apes point back to a common origin from some 
more or less intermediate type. The dental formula of the 
Anthropoid Apes appears to be comparatively fixed; but the 
oY 
@ vi a. \ 
Fic. 97.—-HuMaN MovutvH, IN WHICH THE DEVELOPMENT OF THE UPPER OUTER 
INCISORS HAS BEEN SUPPRESSED. 
v’., inner incisors ; 7”., outer incisors ; p.m., first premolar of the upper jaw ; c., upper 
canines which, under the special conditions, come next in order to the upper inner 
incisors. 
teeth of Man show indications of gradual reduction, especially 
in the variations in the size of the molars and of the upper outer 
INCISOYS. 
The upper outer incisor shows every transition form between 
a well-developed typical tooth and a short conical stump. In 
many individuals, however, this tooth is altogether wanting (cf. 
Fig. 97), and this dental variation may be hereditarily trans- 
mitted through several generations. 
The recent researches of Rose have revealed reason for 
believing that the upper molars of Man have been derived from 
a four-cusped tooth type, and the lower from a five-cusped type, 
and that the numerical reduction of these cusps has been due to 
