The muscles of mastication and the movements of the skull in Lacertilia. 479 
origin the fibres pass outwards and somewhat downwards, in a radiating 
manner, to find insertion to the full extent of the upper and lower 
surfaces of the pterygoid bone from its posterior extremity to as far 
forwards as a level with the articulation between the basipterygoid 
process of the sphenoid and the pterygoid bone. 
M. pterygo-parietalis (Fig. 4 M.pt.-par). 
This, the second muscle of the trio, is smaller than the foregoing, 
and lies on a level immediately internal to that of the columella. It 
arises, by means of a flattened thin tendon, from the downward pro- 
jecting border of the parietal bone. Its insertion is to the upper sur- 
face of the pterygoid immediately in front of the articulation for the 
columella. 
It is especially desired to direct attention to the foregoing two 
muscles for two reasons. Firstly, because of their unquestionable 
homology with two similar muscles in the snakes. In the latter 
animals the muscles are certainly directed somewhat differently, but 
this is due to the greater backward projection of the pterygoid bone. 
Putting this difference on one side, the similarity is striking, and for 
this reason the names as used in Ophidian myology (vide KATHA- 
RINER, 18) have been applied in the above descriptions (cf. Figs. 5 and 6). 
Functional resemblance will be pointed out later. 
The second reason for desiring to draw particular attention to 
these muscles is because of the fact that a description of them is not 
always forthcoming in the literature. I find no reference made to 
them by Horrmann (11). The only references I can find are two. 
STANNIUS (12) in speaking of those reptiles possessed of a columella, 
says: “Ein Hebenmuskel des Os pterygoideum ist vorhanden in einem 
hinter der Columella und einwärts von ihr von der Ala temporalis zu 
seiner Oberfläche gerade absteigenden Muskel: M. levator ossis 
pterygoidei.” And SANDERS (3) calls attention to two muscles which 
lie internal to the M. int. pterygoid. in Platydactylus japonicus: 
“|. the more external arises from a point at the lower surface of 
the parietal, just above the articulation of the prootic with the 
columella, covered in by the membrane which connects the upper edge 
of that bone with the parietal, at the point of attachment of the 
membrane corresponding to the alisphenoid, and is inserted into the 
upper border of the pterygoid, behind the columella. The other 
muscle is internal, and arises from the membranous alisphenoid, be- 
neath the last, in front of the exit of the third division of the fifth 
