D2, CONTRIBUTIONS TO PALALONTOLOGY 
More in detail, the body of the mandible is deep and thin and there is a 
small but sharply defined geniohyoid fossa on the lower border on either side 
of the interdigastric spine; there is hardly any mental eminence. The pit 
for the genioglossal muscles is very shallow. Thus the present symphyseal 
region differs widely from that of Swvapithecus sivalensis, especially in its 
lack of emphasis of the lingual torus and in the delicacy of the lower border. 
DISCUSSION AND SUMMARY 
In previous papers several species of Indian fossil anthropoids have been 
tentatively referred to the genus Dryopithecus, although in the paper on the 
dentition of that genus (1926) two of us suggested that the Indian forms 
were more advanced than the typical Dryoyithecus fontani of Europe and 
probably deserved separate generic rank. The additional material now 
available further emphasizes the contrast in dimensions of the lower molars 
between Dryomthecus fontani and Sivapithecus sivalensis and other Indian 
species. The comparative measurements also show that the depth of the 
mandible between M1 and M2 is relatively greater in the European than in 
the Siwalik members of the “Dryopithecus” group. 
The most primitive known upper molars of the “Dryopithecus” group are 
probably those of Proconsul africanus, as described by Hopwood. These 
retain a good many of the still older tarsioid features, which are clearly ex- 
emplified in the Middle Eocene Periconodon helveticus Stehlin (1916) and 
of which traces evidently persist in Proconsul. The latter, however, as 
befits its far more recent age (?Lower Miocene), has advanced beyond 
Periconodon and toward the Dryopithecus pattern of the upper molars in 
the following respects: (1) the size as a whole is several times greater; 
(2) the interdental triangular embrasures are almost eliminated; (3) the 
hypocones of M1, M2 have become large and now project posteriorly, es- 
pecially in M2; (4) the narrow valley between the crista obliqua (con- 
necting the proto- and metacones) and the posterior cingulum has become 
constricted, giving rise to the fovea posterior; (5) the parastyle at the 
anteroexternal corner of the tooth has virtually disappeared, leaving only 
the outer end of the anterior cingulum; (6) the external cingulum has vir- 
tually disappeared, but the internal cingulum is still well defined. 
In Stvapithecus the four main cusps of the first and second upper molars 
have become swollen and the crown as a whole is higher, the cusps blunter, 
the cingula have disappeared, and the crista obliqua is less prominent. In 
the third upper molar the hypocone and posterior rim have become much 
larger and more prominent. The orang and Grgantopithecus carry these 
specializations still farther. 
The body of the mandible among recent anthropoids is vertically shallow 
in the gibbons and their allies, while that of the orangs is very deep. Like- 
wise among fossil apes the mandible of Dryopithecus fontant is very deep, 
while that of Bramamthecus thorpei is quite shallow. In Srwvagthecus the 
mandible is relatively shallower than in the true Dryopthecus of Europe. 
