ADAMS, PHYLOGENY OF THE JAW MUSCLES 95 



Pterygoideus posterior. — This muscle (called pterygoideus posterior by 

 Lubosch, who also includes a small slip that joins the capiti-mandibu- 

 laris), arises on the quadratojugal and quadrate and joins with the an- 

 terior slip to be inserted on the mandible. A small slip from this joins 

 the temporal mass and is designated as the profundus in this paper. 

 These pterygoid muscles wrap around the posterior end of the mandible, 

 where they swell out, making a large mass on the postero-ventral side of 

 the jaw. This enlargement of the muscle at its insertion is paralleled in 

 Cryptobranchus, as observed by Lubosch (1914, p. 698), who says: "Der 

 Pterygoideus, zerfallt seiner Innervation nach wiederum in zwei Kom- 

 plexe, der Pterygoideus anterior und cler Pterygoideus posterior,, worin 

 tibereinstimmung mit Verhaltnissen der Urodelen besteht." 



MUSCLES OF TEE DEPRESSOR OR DIGASTRIC GROUP 

 (INNERVATED BY VII) 



Depressor mandibular. — This is the typical depressor of the reptiles, 

 arising on the parietal, squamosal and exoccipital. It is firmly inserted 

 on the posterior prolongation of the articular. 



IGUANA 



Plate VII, Figs. 1, 2 



The skull of Iguana is of the streptostylic type, although it is quite 

 solidly constructed and much less specialized than that of Varanus. 

 There is very little movement in the quadrate and pterygoid region, so 

 that the muscles that move these parts in Varanus are not differentiated. 

 The rest of the jaw musculature is very similar to that of Varanus, which 

 is more fully described under its section in this paper. The fenestration 

 in the temporal region of the skull of Iguana is similar to that of Varanus, 

 with a large supratemporal fenestra and with a large sinus below the 

 postorbital and squamosal, this giving the muscles plenty of room to 

 expand. The skull has accommodated itself to the muscles in several 

 ways. The supratemporal fenestra is large and the parietal has expanded 

 dorsally and posteriorly to make a large origin for the capiti-mandibu- 

 laris. 



MUSCLES OF THE ADDUCTOR OR TEMPORAL GROUP 

 (INNERVATED BY V 3 ) 



Capiti-mandibularis. 



(a) Capiti-mandibularis superficialis. 

 — Masseter slip. 



