ADAMS, PHYLOOENY OF THE JAW MUSCLES 119 



HOMO 

 Plate X, Figs. 7, 8 



Eiegner (1906) gives the results of some interesting experiments that 

 he had made upon chloroformed apes. He stimulated the jaw muscles 

 of the unconscious apes and watched the jaw actions, which may be 

 summarized as follows : 



The masseter lifts the jaw and pulls it laterally. 



The temporalis lifts the opened jaw. 



The pterygoideus externus opens the closed jaw to some extent, 

 pulling it slightly medianward and toward the opposite side. 



The pterygoideus internus closes or lifts the open jaw and pulls 

 in opposition to the masseter, i. e., toward the opposite side. 



The digastric (anterior belly) opens the jaw. Without it a nom- 

 inal movement to the opposite side takes place. The hinder belly 

 has little to do with the jaw movements in the ape. 



The geniohj'oid gives the jaw a straight pull in opening it. 



This work on the apes gives about the action that takes place in man, 

 but it is not an entirely accurate account of what happens in some of the 

 mammals with a different type of skull (see also Strasser, 1908). 



MUSCLES OF THE ADDUCTOR OR TEMPORAL GROUP 

 (INNERVATED BY V^) 



Masseter Pterygoideus internus 



Temporalis Digastricus (pars anterior) 



Pterygoideus externus 



MUSCLES OP THE DEPRESSOR OR DIGASTRIC GROUP 

 (INNERVATED BY VII) 



Digastricus (pars posterior) 



MUSCLES OF THE ADDUCTOR OR TEMPORAL GROUP 

 (INNERVATED BY V,) 



Masseter. — Arises from the lower border and inner surface of the 

 zygomatic arch and is inserted on the outer face of the posterior end of 

 the mandible and on the coronoid process. 



Temporalis. — Arises from the whole surface of the temporal fossa, ex- 

 tends down under the zygomatic arch and attaches itself to a point of the 

 coronoid process, the insertion extending slightly down on both sides. 



Pterygoideus externus. — Arises by two heads, from the under surface 



