134 ANNALS NEW YORK ACADEMY OF SCIENCES 



MUSCLES OF THE DEPRESSOR OR DIGASTRIC GROUP 

 (INNERVATED BY VII) 



This muscle is constant in the Reptilia and its insertion is evident on 

 the specimen No. 5027, American Museum. In many reptiles where the 

 back part of the skull is not greatly modified its origin is on the parietal, 

 but here it seems to have been on the paroccipital. The muscle arose on 

 the ventral end of the paroccipitals, the ventral ends of which are rough- 

 ened for a muscle insertion. Its insertion on the mandible was on the 

 articular, posterior to the articulating surface, where there is a depression 

 similar to that seen in most reptiles. 



Cyn'OGNATHUS 



Plate XIII, Figs. 2-5 



The skull is reptilian as a whole, but parts of it very plainly show the 

 mammalian characters, especially the squamosal, the jugal, the dentition 

 and the basicranial region. The quadrate is reduced. The jaw, although 

 reptilian, is of a type that foreshadows that of mammals. The dentary 

 had enlarged from the primitively slender dentary of the early reptiles 

 until it was the most important part of the mandible and must have car- 

 ried the greater part of the musculature. The coronoid process of the 

 dentary is large and ascends far into the temporal fossa. The angle of 

 the dentary is developing and shows plainly. The posterior part of the 

 jaw, consisting of the articular and other elements, is becoming small 

 and is so loosely attached to the dentary that in fossil specimens it is 

 usually missing or found separate from the skull. The old reptilian 

 articulation with the skull had become reduced, but was still functional. 

 Although the new articulation with the jaw had not yet been formed, I 

 infer, from the shape of the temporal fossa and from the direction of the 

 muscles, that the jaw was pulled not directly against the quadrate but 

 toward a point above it on the squamosal. 



MUSCLES OF THE ADDUCTOR OR TEMPORAL GROUP 

 (INNERVATED BY V z ) 



Capiti-mandibularis. 



(a) Capiti-mandibularis superficialis. 



(&) Capiti-mandibularis medius. 



(c) Capiti-mandibularis profundus. 

 Pterygoideus anterior. 



