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.

(FIGURE 27.--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.

(FIGURE 28.--Beaver, Lemur and Baboon. 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 (Figure 29) as 236 to 100.
In the Constantinople skull (Figure 29) 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 (Figure 28), 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 drawn through the axis of the face,
between the bones called ethmoid