Mr. A. R. Wallace on the Orang-Utan or Mias of Borneo, 473 



crested skulls, which have been thought to prove the existence 

 of two large species of Orang. The external surface of the skull 

 varies considerably in size, as do also the zygomatic aperture 

 and the temporal muscle ; but they bear no necessary relation to 

 each other, a small muscle often existing with a large cranial 

 surface and vice versa. Now those skulls which have the largest 

 and strongest jaws and the widest zygomatic aperture, have the 

 muscles so large that they meet on the crown of the skull and 

 deposit the bony ridge which separates them, and which is 

 highest in that which has the smallest cranial surface. In those 

 which combine a large surface with comparatively weak jaws and 

 small zygomatic aperture, the muscles on each side do not ex- 

 tend to the crown, a space of from 1 to 2 inches remaining be- 

 tween them, and along their margins small ridges are formed. 

 Intermediate forms are found in which the ridges meet only in 

 the hinder portion of the skull. The form and size of the ridges 

 are therefore independent of age, being sometimes more strongly 

 developed in the less-aged animal. Professor Temminck states 

 that the series of skulls in the Leyden Museum shows the same 

 result. 



Sir James Brooke first noticed these differences in the ridges, 

 and finding that the Dyaks afiirmed that two large species of 

 Orang existed, very naturally concluded that they respectively 

 belonged to them. • Mr. Blyth of Calcutta has adopted this 

 view, considering that the animal possessing the double-crested 

 skull has the large cheek-excrescences, while that with the single- 

 crested skull is deprived of them ; but my specimens, as well as 

 the series at Leyden, show that these various forms of skull 

 belong to one and the same species of animal, in which view 

 Sir James Brooke, after an examination of my specimens, perfectly 

 coincides. I may here mention, that Mr. Blyth has since written 

 to Sir J. Brooke acknowledging the receipt of some skeletons 

 from Sarawak, and stating that he has found a new species 

 among them distinguished by its shorter and more robust limbs 

 and slightly projecting jaws. The great amount of variation, 

 however, which exists in these respects among animals whose 

 external characters are identical, would show that it is not pos- 

 sible to establish a new species on such grounds from a single 

 specimen. As an instance of the extreme variation which occurs 

 in the skull of the fully adult male Orang with cheek-excres- 

 cences, I may mention that the width between the orbits exter- 

 nally is only 4 inches in one specimen and fully 5 in another, 

 while the two animals did not differ 1 inch in their total height. 



The second form of male Orang which I have procured differs 

 so remarkably from the first, that it seems well entitled to be 

 considered a distinct species. The two fully adult specimens 



