lier and more completely than the sides and roof: and the
cartilaginous base ossifies, and becomes soldered into one piece long
before the roof. I conceive then that the base of the skull may be
demonstrated developmentally to be its relatively fixed part, the roof
and sides being relatively moveable.

[Illustration: Fig. 28.--Oblong and prognathous skull of a Negro; side
and front views. One-third of the natural size.]

The same truth is exemplified by the study of the modifications which
the skull undergoes in ascending from the lower animals up to man.

[Illustration: FIG. 29.--Longitudinal and vertical sections of the
skulls of a Beaver ('Castor Canadensis'), a Lemur ('L. Catia'), and a
Baboon ('Cynocephalus Papio'), 'a b', the basicranial axis; 'b c', the
occipital plane; 'i T', the tentorial plane; 'a d', the olfactory plane;
'f e', the basifacial axis; 'c b a', occipital angle; 'T i a', tentorial
angle; 'd a b', olfactory angle; 'e f b', cranio-facial angle; 'g h',
extreme length of the cavity which lodges the cerebral hemispheres or
'cerebral length.' The length of the basicranial axis as to this length,
or, in other words, the proportional length of the line 'g h' to that
of 'a b' taken as 100, in the three skulls, is as follows:--Beaver 70 to
100; Lemur 119 to 100; Baboon 144 to 100. In an adult male Gorilla the
cerebral length is as 170 to the basicranial axis taken as 100, in the
Negro (Fig. 30) as 236 to 100. In the Constantinople skull (Fig. 30) as
266 to 100. The cranial difference between the highest Ape's skull
and the lowest Man's is therefore very strikingly brought out by these
measurements. In the diagram of the Baboon's skull the dotted lines 'd1
d2', etc., give the angles of the Lemur's and Beaver's skull, as laid
down upon the basicranial axis of the Baboon. The line 'a b' has the
same length in each diagram.]

In such a mammal as a Beaver (Fig. 29), a line ('a b'.) drawn through
the bones, termed basioccipital, basisphenoid, and presphenoid, is very
long in proportion to the extreme length of the cavity which contains
the cerebral hemispheres ('g h'.). The plane of the occipital foramen
('b c'.) forms a slightly acute angle with this 'basicranial axis,'
while the plane of the tentorium ('i T'.) is inclined at rather more
than 90 degrees to the 'basicranial axis'; and so is the plane of the
perforated plate ('a d'.), by which the filaments of the olfactory
nerve leave the skull. Again, a line