Lucas.] 
232 
[October 5, 
those of the canines in males, very large. Thus middle-aged 
males are more prognathous than the adults, for in the latter the 
roots of the teeth are somewhat absorbed. In females, increase 
of age is characterized by the convergence of the temporal ridges 
which usually meet in old specimens ; although as noted above 
this is not always the case. The lambdoidal prominences also 
increase, although they never become large, and by their increase 
give a flattened appearance to the back of the cranium, 
males change of age is much more marked than in females. The 
temporal ridges always unite in old animals, occasionally forming 
a low sagittal crest 10 or 12 mm. high. The lambdoidal prom- 
inences also are greatly enlarged and may even form a lambdoidal 
crest which joins the sagittal crest. The back of skull is much 
flattened. The sphenoid is greatly increased in thickness so as 
to appear swollen, and the pterygoids are laterally expanded. In 
many cases the entire joalatal region increases in width so that 
the grinders, which in young specimens are usually placed in 
slightly converging lines, are brought in parallel rows. 1 In two 
extreme cases the difference was as follows : 
between first premolars. 
between last premolars. 
27 mm. 
40 mm. 
Xoung 40 mm. 
Old 33 mm. 
The zygomata also increase in thickness and width with age. 
Individual skulls vary very considerably in certain points as 
the shape, size, and separation of orbits. The supra-orbital ridges 
are larger in some rather young males than in the oldest spec- 
imens. The nasals are quite different in different animals, being 
wide in a few, much compressed in others and in one case entirely 
absent. The foramen magnum hardly has the same shape in any 
two skulls, but as a rule is a little longer in proportion to its 
width in males than in females. These brief notes point clearly 
to the fact that it is extremely dangerous to form a species from 
observations of one or two skulls, and render it very probable 
that many fossil species have been based on individual or sexual 
peculiarities. 
1 A curious feature in the Orang is the tendency to develop an extra molar, usually 
in the lower jaw. One specimen has two large extra molars, but generally there is but 
one small tooth. Perhaps one in eight or nine has this extra tooth. 
