i THE ORANG. 57 



cranial ridge is either single or double, either much or 

 little developed, and the zygomatic aperture varies con- 

 siderably in size. This variation in the proportions of the 

 crania enables us satisfactorily to explain the marked dif- 

 fernce presented by the single-crested and double-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 ne- 

 cessary relation to each other, a small muscle often exist- 

 ing 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 de- 

 posit 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 compara- 

 tively weak jaws, and small zygomatic aperture, the mus- 

 cles, on each side, do not extend to the crown, a space of 

 from 1 to 2 inches remaining 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 dif- 

 ferent from any of these that he concludes them 

 to be specifically distinct; they were respectively 

 3 feet 8J inches and 3 feet 9^ inches high, and 

 possessed no sign of the cheek excrescences, but 

 otherwise resembled the larger kinds. The skull 



