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growth. It is a cKaracteristic of the cranium of the genus Troglodytes from the time of birth 

 to extreme old age : by the prominent superorbital ridge, for example, the skull of the young 

 Chimpanzee with deciduous teeth may be distinguished at a glance from the skull of an Orang 

 at the same immature age ; the genus Pithecus, Geoffr., being as well recognised by the ab- 

 sence, as the genus Troglodytes is by the presence, of this character. The superorbital ridge, 

 which augments the frame of the orbit in the Chimpanzees, and gives a more vertical position 

 to its plane than in the Orangs, and which also supports a thick moveable fold of integument 

 clothed with bushy eyebrows, relates to the greater accuracy and activity of the visual sense, 

 and harmonises with the superior activity and strength of the great African anthropoid apes, 

 as compared with the more slothful species of the Indian Archipelago. We have no grounds, 

 from observation or experiment, to believe the absence or the presence of a prominent super- 

 orbital ridge to be a modifiable character, or one to be gained or lost through the operations 

 of external causes, inducing particular habits through successive generations of a species. It 

 may be concluded therefore that such feeble indication of the superorbital ridge, aided by 

 the expansion of the frontal sinuses, as exists in Man, is as much a specific peculiarity of the 

 Human skull, in the present comparison, as the exaggeration or suppression of this ridge is 

 respectively characteristic of the Chimpanzees and Orangs. 



The equable length of the Human teeth, the concomitant absence of any diastema or break 

 in the series, and of any sexual difference in the development of particular teeth, are to be 

 viewed by the light of actual knowledge as being primitive and unalterable specific peculiari- 

 ties of Man. 



Teeth, at least the ordinary dentine of mammals, are not organized so as to be influenced 

 in their growth by the action of neighbouring muscles : pressure upon their bony sockets 

 may affect the direction of their growth after they are protruded, but not the specific propor- 

 tions and forms of the crowns of teeth of limited and determinate growth. The crown of the 

 great canine tooth of the male Troglodytes Gorilla began to be calcified when its diet was 

 precisely the same as in the female, when both sexes derived their sustenance from the 

 mother's milk. Its growth proceeded and was almost completed before the sexual develop- 

 ment had advanced so as to establish those differences of habits, of force, of muscular exer- 

 cise, which afterwards characterize the two sexes. The whole crown of the great canine is, in 

 fact, calcified before it cuts the gum or displaces its small deciduous predecessor : the weapon 

 is prepared prior to the development of the forces by which it is to be wielded ; it is there- 

 fore a structure fore-ordained, a predetermined character of the Chimpanzee, by which it 

 is made physically superior to Man, and one can as little conceive its development to be a re- 

 sult of external stimulus, or as being influenced by the muscular actions, as the development 

 of the stomach, the testes or the ovaria. 



The two external divergent fangs of the premolar teeth, and the slighter modifications of the 

 crowns of the molars and premolars, appear likewise from the actual results of observation to 

 be equally predetermined and non-modifiable characters. 



No known cause of change productive of varieties of mammalian species could operate in 

 altering the size, the shape, or the connections of the premaxillary bones, which so remarkably 

 distinguish the great Troglodytes Gorilla, not from Man only, but from all other anthropoid 

 apes. We know as little the conditions which protract the period of the obliteration of the 



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