The muscles of mastication and the movements of the skull in Lacertilia. 483 
The connection of the frontal and mandibular segments is indirect, 
the freely moveable quadrate acting as the connecting link. The 
upper end of the quadrate is connected with the frontal segment only; 
but it should be noted that this connection is in close proximity to 
the joint between the ends of the lateral occipital bone and the frontal 
segment, i. e. it occurs practically in that transverse axis of rotation 
to which attention has already been directed. The lower end of the 
quadrate bone has a double articulation. On the one hand it is joined 
to the extremity of the pterygoid bone. On the other hand it carries 
a smooth articular surface for the mandible. It should be rem- 
embered that these two articulations are close to each other. It may 
further be remarked, as a circumstance of some possible moment, that 
the articular surface on the quadrate bone is, speaking in general 
terms, concave from side to side; the corresponding surface on the 
mandible being commensurately convex. This feature seems to be 
associated with the fact that the two halves of the mandible are very 
loosely joined together at the symphysis. It appears not unreasonable 
to expect that in the living animal there is some degree of rotation 
of each half of the mandible about its own long axis. Such a rotation, 
at any rate, can be very readily produced in the fresh skull. In this 
connection it is desired to call attention to what is virtually an 
articulation between the Os complementare of the mandible and the 
pterygoid bone. If the dried skull of Varanus be examined, a smooth, 
nearly flat area will be found on the pterygoid bone just where it 
joins the Os transversum (Fig. 4 E). A similar area will also be 
found on the inner surface of the Os complementare. These surfaces 
are more evident in the recent state, when dissection shows that they 
are covered by a diverticulum of the mucous membrane of the mouth. 
This articulation (if the term may be permitted) was found to be 
particularly obvious in Gecko. There seems to be little reason to 
doubt that it is associated with a possibility of rotation of the mandible. 
Whether it has a deeper morphological significance or not time and 
further investigation alone will show. 
In studying the movements in the skull observations were made 
upon living Lacertæ. It was found, however, to be somewhat difficult 
to come to any definite conclusions and, therefore, the skulls of 
freshly killed animals, with and without the muscles, were also 
examined. In detailing the movements which are possible in such 
preparations the occipital segment will be considered to be fixed; a 
