ADAMS, PHYLOGENY OF THE JAW MUSCLES 101 



tendon and by a fleshy slip ; the tendon is inserted on the coronoid process 

 and the fleshy slip extends along the outside of the mandible. This 

 muscle is the most important of the mandible, as it extends along the 

 side and has a very wide attachment. 



(&) Capiti-mandibularis medius (et profundus) (C. m. et p.). — This 

 muscle, usually called the temporal, is assumed to represent the middle 

 and deep part of the reptilian capiti-mandibularis. The region for its 

 origin is much reduced and there is no room for much differentiation of 

 this part of the muscle. It fills the temporal fossa in the bird. It arises 

 from the bones surrounding the fossa, extends downward, posterior to 

 the postorbital process, and is inserted on the coronoid process of the 

 mandible. 



Pterygoideus anterior (Pt. a.). — This is a large muscle that covers the 

 floor of the skull at the posterior part of the palatines. It arises along 

 this posterior part of the palatines, spreading out over this to a part of 

 the pterygoids and the orbito-sphenoid. The insertion is on the under 

 side of the articular process and along the inner side of the mandible. 

 This muscle pulls inward and forward on the mandible, thus pulling the 

 quadrate forward — a movement that is very important in the Psittaci, 

 where the maxillas are raised with the anterior part of the skull. 



Pterygoideus posterior (Pt. p.). — This is a smaller muscle that crosses 

 the pterygoideus anterior, going under it. It arises on the orbital process 

 of the quadrate and is inserted on the inner side of the mandible near the 

 posterior end. It draws the mandible backward and pulls down on the 

 quadrate, thus aiding in the closing of the jaw. 



MUSCLES OF THE DEPRESSOR OR DIGASTRIC GROUP 

 (INNERVATED BY VII) 



Depressor mandibulce (P. m.). — The depressor of birds is the same as 

 that of reptiles and amphibians, being a part of the C 2 md of Euge and 

 innervated by the seventh nerve. In the birds it is short and thick, more 

 like the same muscle in the Chelonia than like that of Sphenodon or 

 Varanus. It arises on the squamosal as in the Chelonia, as this region 

 has grown out laterally, so that the origin on the parietal is no longer 

 available. It arises along the ridge of the squamosal and is inserted on 

 the retroarticular process as in reptiles. It opens the mandibles with the 

 aid of some of the long, ventral hyoid muscles of the throat region. 



