1855.] Anthropoid Apes J and their relations to Man. 39 



stances favourable to its higher development would be restricted to 

 differences of size, of colour, and other characters of the hair, and 

 of the shape of the head, in so far as this is influenced by the arrest 

 of general growth after the acquisition by the brain of its mature 

 proportions, and by the development, or otherwise, of processes, 

 crests, and ridges for the attachment of muscles. The most striking 

 deviations from the form of the human cranium which that part 

 presents in the great orangs and chimpanzees result from the latter 

 acknowledged modifiable characters, and might be similarly produ- 

 ced ; but not every deviation from the cranial structure of man, 

 nor any of the important ones upon which the naturalist relies for 

 the determination of the genera troglodytes and pithectis, have such 

 an origin or dependent relation. The great chimpanzee, indeed, 

 differs specifically from both the orang and man in one cranial 

 character, which no difference of diet, habit, or muscular exertion 

 can be conceived to affect. 



The prominent superorbital ridge, for example, is not the con- 

 sequence or concomitant of muscular development ; there are no 

 muscles attached to it that could have excited its growth. It is a 

 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 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 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 particular 

 habits through successive generations of a species. It may be con- 

 cluded, 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, and 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 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 



