MYOLOGY 77 



Action. — It aids in closing the jaw. 



Masseter (Fig. 19, No. i). Location. — Occupies the supero-Iat- 

 eral portion of the surface of the lower jaw. 



Origin. — In two portions: the first, by a broad and thin tendon 

 from the entire length of the bony ridge above the external auditory 

 meatus, from the squamosal process, and from the outer portion of 

 the quadrate bone; the second, from the side and under border of 

 the zygoma. 



Insertion. — ^The first portion: The fibers pass downward and for- 

 ward beneath the zygoma; a few of the fibers blend with those of the 

 temporal; one tendon inserts to a small tubercle on the upper border 

 of the jaw behind the coronoid process, and by fleshy insertion 

 to the outer side of the ramus of the lower jaw, quite as far forward 

 as the homy portion of the beak. The second portion: by a smaU 

 tendon to the mandible on its upper border immediately in front of 

 the articular portion. 



Shape. — Flat, and elongate. Somewhat fleshy. 



Relations. — Superiorly with the temporal, and inferiorly with the 

 biventer maxiUae and stylo-hyoideus. Externally with the skin, 

 and internally with the jaw bone. 



Action. — ^Aids in closing the jaw. 



Biventer Maxillae (Fig. 19, No. 3). Location. — Covers the outer 

 posterior portion of the mandible. 



Origin. — It arises in two portions: The first, from a ridge boimding 

 the posterior part of the auditory canal; the second, from a depres- 

 sion of the mesial side. These two parts blend and extend downward 

 and forward. 



Insertion. — To the posterior part of the articular end of the 

 mandible. 



Shape. — ^A curved fleshy mass. 



Relations. — Superiorly with the temporal and stylo-hyoideus. 

 Posteriorly with the digastricus and genio-hyoideus. Internally 

 with the jaw bone, and externally with the skin. 



Action. — It aids in opening the jaw. 



Entotympanic. Location. — Posterior to the pterygoid. 



Origin. — From the side of the basi-sphenoid and from the base of 

 the rostrum immediately beyond it. 



Insertion. — The fibers pass downward and forward, and insert by a 

 double tendinous slip. One slip inserts to a spine-like process on 



