ADAMS, PHYLOGENY OF THE JAW MUSCLES 97 



(c) Capiti-maiidibularis profundus (C. m. p.). — This muscle is the 

 homologue of the muscle of the same name in Varanus and is strongly 

 developed in reptiles with a columella cranii (epipterygoid). It arises 

 on the outer face of the epipterygoid and on the outer face of the ptery- 

 goid, extends ventrally, and is inserted on the mandible on the lower part 

 of the posterior inner face of the mandible. 



Pterygoideu^ anterior (Pt. a.). — This arises on the pterygoid and 

 wraps around the end of the mandible. The origin is on the under side 

 of the pterygoid; from there it extends around the end of the mandible, 

 making a large belly at the posterior ventral end. It is inserted along 

 the ventral face of the angular and wraps around the articular, so that it 

 is on the inside of the mandible at the posterior end. 



MUSCLES OF THE DEPRESSOR OR DIGASTRIC GROUP 

 (INNERVATED BY Til) 



Depressor mandihulce (D. m.). — This muscle arises on the posterior 

 face of the parietal, extends ventrally, and is inserted on the retroar- 

 ticular process of the mandible. 



VARANUS 

 Plate YII, Figs. 3, 4, 5 



The almost snake-like skull of Varanus is a typical example of the 

 streptostylic skull, with the bones of the skull more or less movable, espe- 

 cially in the quadrate region. There is a joint between the frontals and 

 the parietals which has possibilities of movement, while the quadrate 

 with its loose articulation on the squamosal and pterygoid forms another 

 movable element. In fact the jaws, pterygo-palatine, and the quadrate 

 region are all movable, with the posterior part of the skull as a base. 

 The fenestra are large so that the muscles have room for development. 

 The large supratemporal fenestra serves as the origin of the temporal 

 slip of the capiti-mandibularis, while the lateral fenestra gives it room 

 for development. This fenestration approaches the ophidian type where 

 the opening out has been complete. 



The musculature of the pterygoid region is very musch specialized in 

 the streptostylic forms and is a ca?notelic character. These special 

 muscles could not have been present in the cotylosaurs or stegocephalians, 

 where there is no need of them, as the skull is rigid. The special muscles 

 for moving the upper jaw and the facial part of the skull arise on the 

 parietals, epipterygoid and basisphenoid and are attached along the wliole 

 upper surface of the pterygoid from the articulation with the transverse 



