OF THE ORANG UTANS. 167 
In the human subject the permanent teeth come into place and use in the following 
order: the first true molares (between the sixth and eighth year) ; the middle lower in- 
cisors, the middle upper incisors, the lateral lower incisors, the lateral upper incisors, 
the canines, the bicuspides, (between the seventh and ninth years) ; the second true 
molares (about the twelfth) ; the third molares (twentieth to thirtieth year). 
In the Orang Utan we see that the second true grinders are in place before the canines, 
or bicuspides, or even the lateral incisors of the upper jaw are shed ; but as regards the 
incisors, there is the same priority in the development of those of the lower jaw as in 
the human subject. The difference in regard to the development of the molares indi- 
cates the greater importance of the large grinders to the young frugivorous Orang, 
as compared with the higher and more omnivorous animal. 
Tt still remains to be determined in what order the bicuspides, last molares, and canines 
succeed each other. Judging from the state of advancement which they respectively 
exhibit, I should suppose that the huge canines would be the last to acquire their full 
development in the Orang Utan. The intermaxillary bones are still distinct from the 
maxillaries, and it is probable that the suture is not obliterated until the vascular activity 
in the neighbouring bone is excited by the passage into place of the permanent canine 
teeth. 
The following differences may be observed between the deciduous teeth of the Orang 
and those of the human subject : the first or front incisors of the upper jaw are twice 
as large, and the fangs are proportionally flatter and broader ; the lateral incisors very 
slightly exceed in size those of the human subject, but are directed more obliquely in- 
wards or towards the middle incisors. he four lower incisors of the Orang are nearly 
twice the size of those of the human subject, and differ in the relative position of the 
lateral pair which converge more obliquely towards the middle pair. The canines are 
also nearly double the size of those of the human subject, and project beyond the level 
of the cutting surfaces of the contiguous incisors, from which they are separated by a 
short diastema. The difference in size is much less considerable in the deciduous mo- 
lares ; it is most marked in the superior development of the second inferior molar of 
the Orang. The grinding surface of the anterior molars in the Orang is divided into 
two facets rising towards a middle transverse ridge, while the corresponding part of the 
grinding surface in the human first deciduous molar of the lower jaw is occupied by a 
depression. 
Before proceeding to the description of the cranium of the adult Orang, which I take 
to belong to an unknown species of Simia, Erxl., I shall premise a few observations on 
those species, of the existence of which we have evidences from descriptions and speci- 
mens of the entire individuals, both young and full grown. 
The two great islands of the Indian Ocean, Borneo and Sumatra, are each inhabited 
z2 
