. Bulletin. Natural history; Natuurlijke historie. 66 PEABODY MUSEUM BULLETIN 31 They will not articulate with each other because the bicanine diameter of NMK 190,1 is a little too small to encompass the lateral incisors of UMP 62-11. This is hardly surprising since they come from different individuals from sites separated geographically and possibly temporally, too. What is perhaps more surprising is their similarity. The mandibular symphysis of NMK 190,1 is of some interest. This was de- scribed by Clark and Leakey (1951, p. 60) and figured by them (p. 59). A longitudinal cross section of th
. Bulletin. Natural history; Natuurlijke historie. 66 PEABODY MUSEUM BULLETIN 31 They will not articulate with each other because the bicanine diameter of NMK 190,1 is a little too small to encompass the lateral incisors of UMP 62-11. This is hardly surprising since they come from different individuals from sites separated geographically and possibly temporally, too. What is perhaps more surprising is their similarity. The mandibular symphysis of NMK 190,1 is of some interest. This was de- scribed by Clark and Leakey (1951, p. 60) and figured by them (p. 59). A longitudinal cross section of this symphysis is figured in Leakey (1967, p. 160, fig. 5a) and is also shown in Figure 3. The symphysis is approximately triangular in cross section, with a long planum alveolare gently sloping to the superior trans- verse torus, the most posterior point of which is opposite P4. The internal contour then slopes inferiorly and anteriorly to the inferior transverse torus. The anterior border of the symphysis is rather straight. The length of this an- terior border from infradentale to gnathion is approximately 52 mm and the symphyseal thickness normal to this dimension approximately 28 mm. It should be emphasized that this is the only complete symphysis of a male D. (P.) major known. The other less complete mandibular remains referred to this species share certain features with this specimen. Thus UMP 62-10/66-01 and BM(NH) M16648 show the thickening of the internal aspect of the mandible anteriorly and the gradual shallowing of the superior internal slope; in addition they have long, gently sloping plana. The infant mandibles from Napak also have these features and show that inferiorly the internal contour of the mandible slopes anteriorly and does not project backwards to form a simian shelf. This symphyseal morphology contrasts with that seen in another African species of Dryopithecus, D. (P.) africanus (Fig. 3). Here the planum slopes Fig. 3 Mid-symphyseal sections of living a
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