TEETH. 



921 



only molar in the smaller Chimpanzee as 

 large as the corresponding tooth in the black 

 varieties of the human subject *, in most of 

 which, especially the Australians, the true 

 molars attain larger dimensions than in the 

 yellow or white races. The four principal 

 cusps, especially the two inner ones, of the 

 first molar of both species of Chimpanzee are 

 more pointed and prolonged than in Man ; a 

 fifth small cusp is developed behind the outer 

 pair, as in the Orangs and the Gibbons, but is 

 less than that in Man. The same additional 

 cusp is present in the second molar, which is 

 seldom seen in Man. The crucial groove on 

 the grinding surface is much less distinct than 

 in Man, not being continued across the ridge 

 connecting the anterior pair of cusps in the 

 Chimpanzee. The crown of the third molar 

 is longer antero-posteriorly from the greater 

 development of the fifth posterior cusp, which, 

 however, is rudimental in comparison with 

 that in the Semnopitheques and Macaques. 

 All the three true molars are supported by 

 two distinct and well developed antero-pos- 

 teriorly compressed divergent fangs, longitu- 

 dinally excavated on the sides turned towards 

 each other ; in the white and yellow races of 

 the human subject these fangs are usually 

 connate in m. 3, and sometimes also in ?. 2. 

 The molar series in both species of Chim- 

 panzee forms a straight line, with a slight ten- 

 dency in the upper jaw to bend in the opposite 

 direction to the well-marked curve which the 

 same series describes in the human subject. 



This difference of arrangement, with the 

 more complex implantation of the premolars, 

 the proportionally larger size of the incisors 

 as compared with the molars ; the still greater 

 relative magnitude of the canines ; and, above 

 all, the sexual distinction in that respect, illus- 

 trated by Jigs. 585. 587., stamp the Chimpan- 

 zees most decisively with not merely specific 

 but generic distinctive characters as compared 

 with Man. For the teeth are fashioned in 

 their shape and proportions in the dark re- 

 cesses of their closed formative alveoli, and 

 do not come into the sphere of operation of 

 external modifying causes until the full size of 

 the crowns has been acquired. The formid- 

 able natural weapons, with which the Creator 

 has armed the powerful males of both species 

 of Chimpanzee, fdrm the compensation for 

 the want of that psychical capacity to forge 

 destructive instruments which has been re- 

 served as the exclusive prerogative of Man. 

 Both Chimpanzees and Orangs differ from 

 the human subject in the order of the de- 

 velopment of the permanent series of teeth ; 

 the second molar (?>/. 2) comes into place 

 before either of the premolars has cut the 

 gum, and the last molar (in. 3) is acquired 

 before the canine. We may well suppose 

 that the larger grinders are earlier required 

 by the frugivorous Chimpanzees and Orangs 

 than by the higher organised omnivorous spe- 

 cies with more numerous and varied resources, 

 and probably one main condition of the earlier 



* See my Odontography, pi. lW,fig. 2, m. 



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 

 (art. QUADRUMANA, Vol. IV. p. 210.; Ccbina:*), 

 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 Mam- 

 malia 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 the young Cebus 

 in^g. 589., which corresponds with that of the 

 human child in fig. 584., i. e. the whole of the 



Fig. 589. 



Deciduous and jjermanent teeth of Cebus. 



deciduous dentition is retained, and the first 

 true molar (m. 1 ) is in place on each side of 

 both jaws. The germs of the other teeth of 

 the permanent series are exposed in the upper 

 jaw ; and the crown of a premolar is found 

 above the third molar in place, as well as 

 above the second and first. As regards number, 

 therefore, the molar series, in Cebus, is interme- 

 diate between that of Mustela (fig. 580., IV.) 

 and Felis (ib. V.) ; the little premolar p.i. in 

 Mustela tells plainly enough which of the four 

 is wanting to complete the typical number 

 in the South American Monkey, and which 

 is the additional premolar distinguishing its 

 dental formula from that of the Old World 

 monkeys and man. By reference to Prof. Vro- 

 lik's article (QUADRUMANA) it will be seen 

 that the eighth genus, including the little 

 Marmoset monkeys (Hapalc, Ouistili), " have 

 only the same number of teeth as the monkeys 



of the Old World, viz. 32, i. j, c. { J, m . 



TC 1 1 



." But the difference is much greater 



than this numerical conformity would intimate. 

 In a young Jacchus penicillatus I find that 

 there are three deciduous molars displaced by 

 three premolars, as in the other South Ame- 

 rican Quadrumana, and that it is the last true 

 molar, m. 3, the development of which is sup- 

 pressed, not the premolar p. 2, and thus these 

 diminutive squirrel-like monkeys actually differ 



* The dental series seems, unluckily, not to have 

 been complete in either of the skulls represented hy 

 the distinguished author of that able article (iius. 

 132, 133). 



