482 O. CHARNOCK BRADLEY, 
lizard such as the Lacerta agilis or L. viridis. It may be stated at 
once that the anterior line of movement a described by NirzscuH does 
not exist. The joint between the frontal and parietal bones is not 
moveable. Certainly in the skull of a lizard such as Lacerta viridis 
a certain bending can be produced in this region; but it is a bending 
resulting from the thinness of the bones and not from any pe- 
culiarity in the line of union of frontal and parietal bones. In the 
larger lizards, and in those with thicker cranial bones, such a bending 
is not possible unless great force be used. 
In describing the movements of the skull it is convenient to con- 
sider it as composed of three segments. The first of these is what 
may be called the occipital segment, consisting of occipital, 
prootic and sphenoid bones. This we place first in point of order 
because, inasmuch as it is a continuation, so to speak, of the verte- 
bral column, it is to be looked upon as that segment which is fixed. 
The second segment we may conveniently speak of as the frontal 
segment; and consists of all those bones comprising the upper jaw 
which lie in front of the occipital segment. The third segment is the 
mandibular, consisting of mandible only. The quadrate and columella 
form connecting links between the segments, and are intimately as- 
sociated with the pterygo-palatine arch. 
The conection between the occipital and frontal segments is partly 
‘cartilaginous but largely membranous; the membranous cranium con- 
tinuing the occipital segment forwards. There is, however, a very 
important synovial joint on each side between the basipterygoid pro- 
cess of the sphenoid and the pterygoid bone. It should be noted 
that the sphenoid with its basipterygoid processes fits like a wedge 
between the two pterygoids. 
Another very important joint is formed by the extremities of the 
lateral occipital bones. These projections are fastened to corresponding 
projections from the frontal segment; and thus two joints are formed 
which lie in a transverse axis about which the frontal segment has 
the power of limited rotation. The joint between the occipital and 
parietal bones is comparatively loose, being formed by fibrous tissue 
except in the middle line where a small cartilaginous projection from 
the supraoccipital meets the parietals. This little process of cartilage 
has been described and figured by Lrypie (16), and doubtless cor- 
responds to the Processus ascendens tecti synotici of the 
primordial cartilaginous cranium as described by GAupp (17). 
