101 



characteristic 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 gorilla or chimpanzee with de- 

 ciduous 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 absence, as the genus Troglodytes is by the 

 presence, of this character. We have no grounds, from observation 

 or experiment, to believe the absence or the presence of a prominent 

 superorbital ridge to be a modifiable character, or one to be gained 

 or lost through the operations of external causes, inducing par- 

 ticular 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 of this 

 ridge is characteristic of the chimpanzees and its suppression of 

 the 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 spe- 

 cific peculiarities of man. 



Teeth, at least such as consist of the ordinary dentine of mam- 

 mals, are not organised 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 pro- 

 truded, but not the specific proportions 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 development 

 had advanced so as to establish those differences of habits, of force, 

 of muscular exercise, which afterwards characterise 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 therefore a structure fore-ordained, a 

 predetermined character of the great ape, by which that creature 

 is made physically superior to man ; and one can as little conceive 

 the development of the canine tooth to be a result of external 



