41 
double-crested skulls, which have been thought to prove the 
existence of two large species of Orang. The external sur- 
face 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 versd. 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 the 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 extend to the crown, a space of from 1 to 2 inches re- 
maining between them, and along their margins small ridges 
are formed. Intermediate forms are found, in which the 
ridges meet only in the hinder part 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.” 
Mr. Wallace observed two male adult Orangs (Mias Kassu 
of the Dyaks), however, so very different from any of these 
that he concludes them to be specifically distinct ; they were 
respectively 3 feet 84 in. and 3 feet 914 inches high, and pos- 
sessed no sign of the cheek excrescences, but otherwise re- 
sembled the larger kinds. The skull has no crest, but two 
bony ridges, 13 inches to 2 inches apart, as in the Stmia 
morio of Professor Owen. The teeth, however, are im- 
mense, equalling or surpassing those of the other species. 
The females of both these kinds, according to Mr. Wallace, 
are devoid of excrescences, and resemble the smaller males, 
but are shorter by 14 to 3 inches, and their canine teeth are 
comparatively small, subtruncated and dilated at the base, as 
in the so-called Simia morio, which is, in all probability, the 
skull of a female of the same species as the smaller males. 
