ADAMS, PHYLOGENY OF THE JAW MUSCLES 77 



Protractor hyomandibularis (P. h.). 

 Dilator opereuli (D. 0.). 



MUSCLES OF THE DEPRESSOR OR DIGASTRIC GROUP 

 (INNERVATED BY VII) 



Levator opereuli (L. 0.). 



MUSCLES OF THE ADDUCTOR OR TEMPORAL GROUP 

 (INNERVATED BY V 3 ) 



The adductor is divided into two layers and a third is present as the 

 intramandibular slip. There is a connection by a rudimentary tendon 

 with one of the anterior levator maxilla? muscles that arises at the anterior 

 of the premaxilla and joins the adductor near its tendon. The main 

 adductor arises along the anterior face of the preoperculum, following 

 down along this bone to its tendon near the mandible. The deeper layer 

 arises on the quadrate and metapterygoid region, joining the rest of the 

 adductor and ending in a crescent-shaped tendon near the coronoid region 

 of the mandible. This connects with the muscle in the mandible (Adm 4 ) 

 which is the Add. w of Vetter. This consists of a mass of fibers attached 

 to the dentar}', with all of the fibers converging to a central tendon, which 

 is connected with the tendon of the main adductor. 



Levator arcus palatini (L. a. p.) . — When the eye is removed this muscle 

 is seen with its fibers extending ventrally to be attached to the palatines 

 and pterygoids. It arises on the parasphenoid and most of the short 

 fibers are inserted with a fleshy attachment to the palatine and a few to 

 the pterygoids. It raises the palatine region. 



Protractor hyomandibularis (P. h.). — This muscle arises on the sphe- 

 notic and extends under the dorsal end of the adductor, to be inserted on 

 the outer face of the hyomandibular. It draws the hyomandibular and 

 opercular apparatus forward. 



Dilator opereuli (D. 0.). — It arises on the sphenotic under the pro- 

 tractor hyomandibularis and extends posteriorly to be inserted on the 

 anterior, dorsal portion of the operculum. It pulls the operculum for- 

 ward and raises it slightly. 



MUSCLES OF THE DEPRESSOR OR DIGASTRIC GROUP 

 (INNERVATED BY VII) 



Levator opereuli (L. 0.). — It arises on the posterior end of the pterotic 

 and extends downward to its insertion on the inside of the upper, inner 

 face of the operculum. It raises the operculum and pulls it slightly 

 forward. 



