PRIMROSE : THE ANATOMY OF THE ORANG OUTANG 
5 
with the skull fairly early. Thus Delisle ^ observes that many crania 
exhibit well-developed sagittal crests, whilst as yet osseous union has 
failed to occur between the basioccipital and the basisphenoid. In 
man this union occurs about the twentieth year. Delisle describes the 
skull of an Orang, which exhibited this and other signs of youth, in 
which the crests were apparently in an early stage of development; 
the frontal crests, instead of uniting at the bregma to form the sagittal 
crest, passed backwards close to the superior border of the parietal 
bones, on each side of the sagittal suture, quite independently of each 
other, being separated by an interval of 2 cm. until they reached the 
occipital crest. This interparietal ridge may rise, according to Owen,^ 
in the adult animal, to the height of one-third to two-thirds of an inch 
above the general surface. These crests give a massive appearance to 
the skull, but as Owen^ long ago showed in his description of the skull 
of a Gorilla, the skull may be actually lighter than it is in man. This 
unexpected result is due to the greater size and extent of the air cells. 
Owen found that these extended in the Gorilla backwards from the 
tympanum, along the base of the occipital crests, as far as their junction 
with the parietal crest, and forwards also to the sphenoidal sinuses ; the 
frontal sinuses, and the antrum, were also developed to an unusual 
extent. 
The dental formula in the Orang is similar to that of man. In my 
specimen none of the permanent teeth had as yet erupted, and the for- 
mula was as follows : — 
{ 2-2 I - I 2-2 
I — - C M = 20 
2-2 I - I 2-2 
One finds that the dental formula in all the anthropoid apes is the same 
as that of man, and, in fact, such is the case in all the old world apes, 
with the exception of the Lemurs ; whilst, on the other hand, among 
the American apes there is considerable variation. 
The lips are very wide and possess a wonderful degree of mobility. 
The mouth, in the living Orang, is said to be closed as a rule ; but, 
when the animal is taking food, the lips are used in a very curious 
I Delisle, “ Sur I’ost^ologie des Orang-Outans.” Comptes Rendus de I’Acad^mie des Sciences. Paris, 
1894, Vol. CXIX, p. 241. 
2 Loc. cit., p. 356. 
3 R. Owen, “ Osteological Contributions to the Natural History of the Chimpanzees, etc.” Transactions 
of the Zoological Society of London, Vol. Ill, 1848, p, 412. 
