The muscles of mastication and the moyements of the skull in Lacertilia. 48] 
used for convenience only. The probability of the comparison of this 
muscle with one in the snakes will be pointed out later. 
The disposition of the muscle in Varanus is as follows. It is 
very thin and takes origin by a thin flat tendon from the parietal 
bone under cover of the origin of the M. pterygo-parietalis, and from 
the membranous cranium in the neighbourhood of the opening for the 
fifth cranial nerve. It sweeps downwards and forwards to the lower 
part of the orbit. There can be little doubt that some of its fibres 
are lost in the lower eyelid; but many of them end in the fibrous 
membrane which closes in the opening circumscribed by pterygoid, 
palatine and transverse bones, and which is exposed when the mucous 
membrane is removed from the roof of the mouth. As a consequence 
it may be said to have an indirect attachment to the skull, as well 
as an insertion into the lower eyelid. It appears, therefore, that 
FiscHeR and WEBER were both partially right, but that each erred 
in the direction of omission. 
A question which suggests itself in connection with this muscle 
is, whether there is any possibility of its being the homologe of the 
M. pterygo-sphenoidalis anterior of snakes (cf. Fig. 6 MZ. pt.sph.ant). 
Does it not seem probable that this is so; and that the differences in 
attachment are due to differences in the mobility of that part of the 
skull to which it is inserted? That this muscle is part of a group is 
shown by its nerve supply. A small nerve (Fig. 4 D), leaving the 
Gasserian ganglion itself (according to FISCHER, 14), or at any rate 
arising from the N. mandibularis as soon as this comes into existence, 
supplies all of the group of three. muscles just described. 
The action of the main jaw-muscles offers little difficulty. That 
the Mm. capiti-mandibularis and pterygoideus are levators of the 
mandible, and that the M. parieto-mandibularis is a depressor is suf- 
ficiently clear. There seems also little reason to doubt that the main 
action of the M. pterygo-mandibularis is to assist the main levators 
of the mandible. But, as has been pointed out long ago by Nrrzscx (7), 
the movements of the jaws do not consist solely in depression and 
elevation of the mandible. As Nirzscu stated, there is an associated 
elevation and depression of the upper jaw. ‘This investigator con- 
sidered that the movement of the upper jaw took place along two 
lines. The first of these he held to be between the frontal and 
parietal bones; and the second between the parietal bone and the 
occipital. That the nature of the movements is not quite so simple 
is abundantly evident if one carefully examines the fresh skull of a 
