IN BORNEAN FORESTS [chap. 



the wider are the " tj apings," or cheek-expansions, the greater 

 is the development of the cranial crest ; and we are led to suppose 

 that there is a sort of correlation and that the first character is 

 the cause of the second one. Of course, the augmented weight of the 

 head and consequent development of the cranial muscles may also 

 contribute to the enlargement of these crests which, as a general 

 rule, grow with age in all the Anthropomorpha. 1 



I do not know of any well-authenticated specimen of the skull 

 of a young orang-utan, during the period of the first dentition, 

 with lateral face expansions, and cannot, therefore, say whether 

 in that stage there are or are not signs of any development of the 

 cranial crests. As far as I am aware no skull of a female orang, 

 of any race, is known with crests. 



I have observed cases of abnormal dentition even in the series 

 of orang-utan skulls which I collected. Thus that of a female 

 Mayas Kassa had two small fourth molars in the lower jaw, 

 and corresponding supernumerary molars in the upper jaw, still 

 enclosed in their alveoli. 



All the orang-utans which I collected — at least all those of which 

 I preserved the skin or the skeleton — were without a nail on the great 

 toe or hallux, or had it reduced to a mere rudiment. Moreover, 

 this peculiarity was associated with the absence of the ungual 

 phalanx in that toe. But specimens of orang-utan are known, both 

 from Borneo and from Sumatra, in which both the nail and the 

 terminal phalanx of the hallux are well developed. Again, it appears 

 that this character is not in any connected with the presence or 

 absence of cheek-expansions, and that there are Mayas Tj aping 

 with, and others without, a nail on their great toes. This has not 

 prevented specific value being given to the character affecting the 

 extremit}^ of the hallux, and the name of Simla bicolor has been con- 

 ferred on those orang-utans which possess a terminal phalanx 

 and a nail on their great toes. 



I may remark that the specimens devoid of these two parts offer 

 an example of the extreme effects of disuse and the non-practice 

 of terrestial locomotion ; the development of the hallux having 

 diminished in importance to the corresponding advantage of that 

 of the other toes, which, under the conditions of a purely arboreal 

 existence, have assumed functions more similar to those of the 

 fingers. 



After all that has been said, what conclusions can we come to 

 regarding the question of a plurality of species amongst the orang- 

 utans ? The answer is much more difficult than anyone who is not 

 a zoologist might be led to suppose. For the laity there are big 



1 It is to be remarked that on the skulls of adult gorillas the develop- 

 ment of bony crests is very conspicuous, although these anthropoids are devoid 

 of fatty cheek-expansions. 



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