AZ)AJ/^^ PHYLOGEXY OF THE JAW 2IUl<CLES 133 



MUSCLES OF THE ADDUCTOR OR TEMPORAL GROUP 

 {INNERVATED BY V^) 



Capiti-manclibularis (with three unseparated slips). 



(a) Capiti-maiulibularis supcrficialis. 



(&) Capiti-mandibularis medius. 



(c) Capiti-mandibularis profundus. 

 Pterygoideus anterior. 



MUSCLES OF THE DEPRESSOR OR DIGASTRIC GROUP 

 (INNERVATED BY VII) 



Depressor mandibula?. 



MUSCLES OF THE ADDUCTOR OR TEMPORAL GROUP 

 {INNERVATED BY V^) 



Capiti-mandibularis. — This muscle is considered to have three slips, 

 designated as superficialis, medius and profundus. They are not com- 

 petely separated in the Eeptilia. The temporal fenestrae show that this 

 muscle had retained its freedom of movement, which it had inherited 

 from some remote aetosaur-like ancestor. There is a long fenestra rmder 

 the eye, a lateral temporal and a supratemporal fenestra. The capiti- 

 mandilmlaris would probably conform to the Alligator or Chelydra type. 

 The presence of the supratemporal fenestra means that the temporal or 

 medius slip extended through and was attached to the parietal crest. 

 Thus the medius slip probably arose on the parietal, extended through 

 tlie supratemporal fenestra and under the superficial slip to be inserted 

 on the coronoid or in the suprameckelian fossa which is large. The 

 superficialis slip would have fibers extending posteriorly over the rest of 

 the mass. This slip would arise on the squamosal, quadratojugal and be 

 inserted along the upper edge of the mandible and in the suprameckelian 

 fossa. In a few forms this muscle is partly inserted on the outside of the 

 mandible, but the outside insertion is small in typical reptiles. A deep 

 slip might have been present, representing the capiti-mandibularis pro- 

 fundus. 



Pterygoideus anterior. — The insertion of this muscle is plainly indi- 

 cated in the mandible of specimen No. 5027, American ]\Iuseum, which 

 shows the place where the anterior pterygoid was wrapped around the 

 posterior end of the jaw as in typical reptiles. The muscle probably arose 

 in the space below and in front of the orbits and above the palatines and 

 pterygoid, as in Alligator. The existence of antorbital fenestra was held 

 by Dollo and by Gregory and Adams (1915) to be correlated with the an- 

 terior extension of the anterior pterygoid muscle — a view adopted here. 



