Vol. 70.] 



LOWER JAW OF AN ANTHROPOID APE. 



319 



Anthropoids. 1 In the latter the digastric muscles are more or less 

 reduced, and Dryopithecus represents the stage in which the 

 reduction had only just begun. 



So far as the shape of its mandible is concerned, Dryopithecus 

 is, therefore, a primitive type ; and it is interesting to add that 

 the relatively small size of its first molar is a character of the 

 Macaques and other monkeys rather than of Anthropoids, although 

 it is observable in some Gibbons. 



A comparison of the mandibular symphysis of Dryopithecus 

 with that of the existing Chimpanzee, Gorilla, and Orang, shows 

 that it is also of a generalized type. In adult individuals of 



Fig. 2. — Cross section of mandibular symphysis of Homo heidel- 

 bergensis (shaded), superposed (a) on that of Eoanthropus 

 dawsoni (outline) and (b) on that of Dryopithecus fontani 

 (outline) ; natural size. Secondary bone at the origin of 

 the geniohyoid muscles dotted. 



these Apes, the lower border of the symphysis is extended back- 

 wards either into a slender bony flange (text-fig. 1 d 2 , d 3 , & e 2 , 

 p. 317) or into a very massive thickening (e 3 ) ; consequently, the 

 anterior face of the bone does not slope abruptly upwards from the 

 front border of the digastric insertion, but only turns upwards after 

 a more or less marked horizontal extension. In other words, the 

 bony chin is antero-posteriorly elongated. In newly-born individuals 

 of all these Apes, however, there is no such elongation or exten- 

 sion, and the anterior face of the symphysis (text-fig. 1 d 1 & e 1 ) 

 slopes upwards almost as abruptly as in Dryopithecus. The Miocene 

 Ape may, therefore, have been a common ancestor of the existing 

 Apes in question. 



The generalized character of the mandibular symphysis of Dryo- 

 pithecus is still further emphasized when comparison is made with 

 that of the oldest known species of Homo (H. heidelbergensis, 



1 M. Holl, ' Zur Morpholog-ie des Musculus digastricus mandibular der 

 Affen' Sitzxingsb. k. Akad. Wiss. Wien, vol. cxxi, sect, iii (1912) pp. 107 & 109. 



Q. J. G. S. No. 279. z 



