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stimulus, or as being influenced by the muscular actions, as the 

 development of the stomach, or of any internal gland. 



The two external divergent fangs of the premolar teeth, and 

 the slighter modifications of the crowns of the molars and pre- 

 molars, 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 con- 

 nexions of the premaxillary bones, which so remarkably distinguish 

 the 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 sutures of the premaxillary 

 bones in the Tr. gorilla beyond the period at which they disappear 

 in the Tr. niger, as we do those that cause them to disappear in 

 man earlier than they do even in the smaller species of chimpanzee. 



There is not, in fact, any other character than those founded 

 upon the developments of bone for the attachment of muscles, which 

 is known to be subject to change through the operation of external 

 causes; nine-tenths, therefore, of the differences, especially those 

 very striking ones manifested by the pelvis and pelvic extremities, 

 which I have cited in the memoirs on the subject, published in the 

 Zoological Transactions, as distinguishing the gorilla and chimpanzee 

 from the human species, must stand in contravention of the hypo- 

 thesis of transmutation and progressive development, until the 

 supporters of that hypothesis are enabled to adduce the facts and 

 cases which demonstrate the conditions of the modifications of such 

 characters. 



If the consideration of the cranial and dental characters of the 

 Troglodytes gorilla has led legitimately to the conclusion that it is 

 specifically distinct from the Troglodytes niger, the hiatus is still 

 greater that divides it from the human species, between the ex- 

 tremest varieties of which there is no osteological and dental 

 distinction which can be compared to that manifested by the shorter 

 premaxillaries and larger incisors of the Troglodytes niger as com- 

 pared with the Tr. gorilla. 



The analogy which the establishment of the second and more 

 formidable species of chimpanzee in Africa has brought to light 

 between the representation of the genus Troglodytes in that con- 

 tinent, and that of the genus Pithecus in the great islands of the 

 Indian Archipelago, is very close and interesting. As the Troglo- 

 dytes gorilla parallels the Pithecus Wurnibii, so the Troglodytes 



