150 
“basifacial axis” (f. e.) forms an exceedingly obtuse angle, 
where, when produced, it cuts the ‘ basicranial axis.’ 
If the angle made by the line 8. c. witha. d., be called the 
‘ occipital angle,’ and the angle made by the line a. d. with a. 6. 
be termed the ‘olfactory angle’ and that made by i. T. with a. d. 
the ‘tentorial angle’ then all these, in the mammal in ques- 
tion, are nearly right angles, varying between 80° and 110°. 
The angle e. f. 6., or that made by the cranial with the 
facial axis, and which may be termed the ‘ cranio-facial 
angle,’ is extremely obtuse, amounting, in the case of the 
Beaver, to at least 150°. 
But if a series of sections of mammalian skulls, intermediate 
between a Rodent and a Man (Fig. 29), be examined, it will 
be found that in the higher crania the basi-cranial axis 
becomes shorter relatively to the cerebral length; that the 
‘olfactory angle’ and ‘ occipital angle’ become more obtuse ; 
and that the ‘ cranio-facial angle,’ becomes more acute by 
the bending down, as it were, of the facial axis upon the 
cranial axis. At the same time, the roof of the cranium be- 
comes more and more arched, to allow of the increasing 
height of the cerebral hemispheres, which is eminently 
characteristic of man, as well as of that backward extension, 
beyond the cerebellum, which reaches its maximum in the 
South American Monkeys. So that, at last, in the human 
skull (Fig. 30), the cerebral length is between twice and 
thrice as great as the length of the basicranial axis; the 
olfactory plane is 20° or 30° on the under sideof that axis; 
the occipital angle, instead of being less than 90°, is as much 
as 150° or 160°; the cranio-facial angle may be 90° or less, 
and the vertical height of the skull may have a large propor- 
tion to its length. 
It will be obvious, from an inspection of the diagrams, 
that the basicranial axis is, in the ascending series of Mam- 
malia, a relatively fixed line, on which the bones of the 
sides and roof of the cranial cavity, and of the face, may be 
said to revolve downwards and forwards or backwards, accord- 
