378 MR. R. OWEN ON THE OSTEOLOGY OF 
contour of the two skulls is greater than is usually observable in those of other wild 
animals of the same species, yet I do not consider them sufficient to afford grounds for 
specific distinction. It is probable, however, that they may be indicative of varieties of 
the Orang inhabiting distinct localities ; and it would be interesting with that view to 
compare the crania of ascertained specimens from Borneo and Sumatra, to which islands 
this very remarkable animal appears to be confined. 
PLATE LIV. 
Base of the skull of the adult Orang Utan: atog, Rudiments of the permanent teeth 
taken from the jaws of an immature specimen. 
PLATE LV. 
Fig. 1. Side view of the skull of a young Chimpanzee. 
Fig. 2. Side view of the skull of a young Orang Utan. These views are both of 
the natural size, and taken at corresponding periods of dentition, when the permanent 
teeth are advanced to the extent shown in the preceding figures. 
PLATE LVI. 
Comparative views of the skulls of the young and old Chimpanzee and Orang Utan, 
showing the changes of form they respectively undergo in attaining to maturity. 
Figg. 1, 5. Young Chimpanzee. 
2, 6. Adult Chimpanzee. 
3, 7. Young Orang Utan. 
4, 8. Adult Orang Utan. 
A comparison of Fig. 1 with Fig. 2, and of Fig. 3 with Fig. 4, will show that those 
differences between the young and old skulls that are present in the Simia Satyrus, and 
which have been chiefly insisted upon as proofs of a specific difference between them, 
obtain equally in the Simia Troglodytes. 
Dr. Harwood (loc. cit., p. 474,) observes, ‘“‘ But the most distinguishing difference 
relates to the proportions of the orbits, and the space which separates them. ‘They are 
of by far the greatest proportionate size in the Satyrus; for in the very young animals 
before alluded to they measure transversely 15 lines and a half, while in the skull of the 
largest Pongo ever brought to this country, they extend no more than 17 lines and a 
half. But the difference in the extent of the space between the orbits is of all the di- 
stinctions I have seen the most apparent ; for in the Satyrus, where the transverse ex- 
tent of the orbits is 15 lines and a half, and the vertical 17 and a half, the space between 
the orbits is only 2 lines and a half; and in thestill younger Satyrus at the Royal Insti- 
