from the true cranial capacity by more than perhaps 10 to 20 c.c. in either 

 direction. 



The endocast was varnished and its volume determined by displace- 

 ment of water. In 7 determinations the displaced water was measured by 

 volume and in 3 further determinations by weight. The mean of the first 7 

 estimations was 529.7 c.c; the mean of the next 3 estimations was 528.1 c.c; 

 and the overall mean for 10 estimations was 529.2 c.c. For practical pur- 

 poses, I have accepted the value of 530 c.c. (Tobias 1963, 1967a). 



This Olduvai australopithecine falls somewhat short of full adulthood, 

 the third molars being not yet in the fully erupted position of occlusion. 

 The age of the youth may have been fifteen to sixteen years. Very little, if 

 any, further growth of the brain occurs after this age. In modern man, for 

 instance, brain growth is said to end at about twenty or twenty-one years of 

 age (Marchand 1902, Pfister 1903, Zuckerman 1928), although a few 

 workers would extend the period of growth somewhat longer (Zuckerman 

 1928). For chimpanzee, Zuckerman found that "there is evidence for con- 

 tinuation of growth into the resting stage preceding the eruption of the 

 third molar" (1928, p. 21). Earlier (p. 17) he states, "All the evidence sug- 

 gests a possible continuation of growth [in capacity of chimpanzee crania] 

 until the stage preceding the eruption of the third molars, but there is no 

 evidence as yet for any growth after that period." Old. Horn. 5 is precisely 

 at the stage immediately preceding the complete eruption of the third 

 molars. 



Zuckerman's conclusions about the dental age at which growth of the 

 cranial capacity ceases received some support from the data of Ashton and 

 Spence (1958), although in their study all crania between the stage of 

 eruption of the first molars and the completion of the permanent dentition 

 were lumped into a single category. 



According to Weidenreich (1941, p. 414), the cessation of actual brain 

 growth coincides in man and pongids with the eruption of the third molar. 

 In the light of these comparative data, since Old. Horn. 5 is almost dentally 

 mature, the value of 530 c.c. may be accepted as the adult cranial ca- 

 pacity. 



Thus, the value for A. boisei coincides with that obtained by Holloway 

 for the Swartkrans endocast of A. robustus and with the capacity of the 

 largest-brained of the 4 Sterkfontein specimens for which capacity esti- 

 mates are available. It is, on the other hand, slightly bigger than the middle 

 value for the Swartkrans specimen (500 c.c). 



^ 26 



