MYOLOGY 29 



(6) The ental head has origin from the orbital surface 

 of the septum of the maxillary root of the zygoma and the 

 inner border of the arch. It develops an aponeurosis upon 

 its ental bell}'', to which are attached the fibers of the infra- 

 orbital head as well as a few from the temporalis, and the 

 narrow insertion is mainly in a line extending from the 

 anterior termination of the masseteric ridge to the base of 

 the mandibular condyle. 



(c) The infraorbital head has origin from the infraorbital 

 fossa, and passing caudad through the infraorbital fora- 

 men, descends and is inserted upon the medial surface of 

 the aponeurosis of the ental head. 



M. temporalis (figs. 6, 23, 24, 25) is imperfectly divisible 

 into two portions, least well developed in Homodontomys, 

 slightl}^ better in Neotoma, and best in Teonoma. The 

 more superficial and anterior part arises from the tem- 

 poral ridge almost as far caudad as the interparietal. 

 The posterior border is very thin, and to a slight extent 

 aponeurotic. Some of the ental fibers are inserted upon 

 the superficial surface of the aponeurotic sheet covering the 

 deep division, making the two difficult to separate at this 

 point. Passing within the orbit, it is inserted upon the 

 ental surface of the coronoid process of the mandible and 

 its root, and also upon the aponeurosis descending from the 

 ental division of the masseter major. 



The posterior or deep part of the temporal arises from 

 that portion of the temporal ridge and fossa immediately 

 laterad of the interparietal, from the lambdoidal crest and 

 the part of the temporal fossa cranio-ventrad thereto. 

 The ventro-lateral portion bulges well over the zygomatic 

 process of the squamosal but it is not attached at this 

 point. As it descends craniad, a superficial aponeurosis 

 develops, which converges to a tendinous insertion upon 

 the tip of the mandibular coronoid process and a small part 

 of the ectal surface adjoining. 



