TEETH OF OEANG AND CHIMPANZEE. 305 



ration of external modifying causes, until the full size of 

 the crowns has been acquired. The formidable natural 

 weapons, with which the Creator has armed the powerful 

 males of both species of chimpanzee, form the compensa- 

 tion for the want of that psychical capacity to forge de- 

 structive instruments which has been reserved as the 

 exclusive prerogative of man. Both chimpanzees and 

 orangs differ from the human subject in the order of the 

 development of the permanent series of teeth ; the second 

 molar, in 2, comes into place before either of the pre- 

 molars has cut the gum, and the last molar, m 3, is ac- 

 quired before the canine. We may well suppose that the 

 larger grinders are earlier required by the frugivorous 

 chimpanzees and orangs than by the higher organized 

 omnivorous species with more numerous and varied re- 

 sources ; and probably one main condition of the earlier 

 development of the canines and premolars in man may 

 be their smaller relative size. 



In the South American quadrumana, the number of 

 teeth is increased to thirty six, by an addition of one 

 tooth to the molar series on each side of both jaws. It 

 might be concluded, a priori^ that as three is the typical 

 number of true molars in the placental mammalia with 

 two sets of teeth, the additional tooth in the cebince would 

 be a premolar, and form one step to the resumption of the 

 normal number (four) of that kind of teeth. The proof 

 of the accuracy of this inference is given by the state of 

 the dentition in any young spider-monkey (Ateles), or 

 Capucin-monkey {Cehus\ which may correspond with that 

 of the human child in Fig. 76, i. e. where the whole of the 

 deciduous dentition is retained, together with the first 

 true molar (w 1) on each side of both jaws. If the germs 

 of the other teeth of the permanent series be exposed in 



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