484 O0. CHARNOCK BRADLEY, 
condition which doubtless prevails during life. The occipital segment, 
therefore, being fixed, it will be found that, in addition to the ordinary 
and obvious movements of depression and elevation of the mandible, 
a certain ‘amount of movement is possible in the upper jaw. This 
consists of movement of the frontal portion in the segment of a circle 
whose centre lies in the transverse axis which joins the posterior part 
of the two lateral occipital bones. In other words there is a movement 
of elevation and depression corresponding to that described by 
Nırzsch (7) as existing in his posterior “Biegungslinie’. During 
elevation of the frontal segment it will be found that the pterygoid 
bones are adducted towards the middle line. This can be noticed in 
the living animal, or in the intact head of an animal recently dead, 
when the mouth is widely opened. This adduction is most obvious 
in the pterygoid bones, but it is not confined to them. The movement 
is shared in by the palatine, transverse and superior maxillary bones ; 
the degree of movement becoming gradually less towards the anterior 
end of the series. The intermaxillary bone is fixed. Because of the 
articulation of the lower end of the quadrate with the posterior ex- 
tremity of the pterygoid, it is also drawn towards the middle line; 
and, consequently, the posterior ends of the two halves of the mandible 
are likewise adducted. To sum up, the effect is as follows. Least 
movement -occurs in the neighbourhood of the ends of the projecting 
lateral occipitals ; in which region, it may be remarked, are the upper 
ends of the quadrate bones. There is elevation of the frontal segment 
at the same time as the mandible is depressed; and concurrently 
there is a narrowing of the mouth, which narrowing is greatest 
posteriorly. 
When the mouth is closed the parts are restored to the condition 
of rest; i. e. there is depression of the frontal segment, and abduction 
of the pterygo-palatine arch, the lower end of the quadrate and the 
posterior part of the mandible. This results in an increase in the 
transverse diameter of the mouth, the increase being greatest post- 
eriorly. If the frontal segment be more forcibly depressed the basi- 
pterygoid processes of the sphenoid exert their wedge-like action upon 
the pterygoids, so producing further abduction. Therefore, when the 
frontal segment is depressed the transverse diameter of the mouth is 
increased. : 
The importance of the movements of adduction and abduction of 
jaws becomes evident when we consider the nature and condition of 
the food of lizards. In the first place it should be borne in mind 
