94 



PRACTICAL ANATOMY. 



active in assisting the external pterygoid muscle, in drawing the lower molars 

 across the upper molars, in trituration of food ; the other the deep portion 

 is weak, broad, muscular, and almost passive in assisting the posterior segment 

 of the temporal muscle in bringing the mandible back to its position, preparatory 

 to another movement of trituration. 



The specific origins and insertions of these separate parts of the masseter 

 muscle make possible the separate physiological functions, as above indicated. 

 Study them separately, as follows : 



The superficial part of the masseter (Fig. 56) muscle arises: (i) From 



Corrugatpr 

 supercilii 



Fyramidalis 



Levator labii 



Buperioris 



alaequc nasi 



Levator labii 



Buperioris 



Compressor 



uarium 

 Levator anguli 



oria 



Naso-labialis 

 Depressor alae 



nasi 

 Orbicularis oris 



Buccinator 



Depressor 



anguli oris 



Depressor labii 



inferioris 

 Levator menti 

 Mylo-hyoid 



Anterior belly of 

 digastric 



Temporal 



Zygomaticus 

 major 



Posterior belly 

 of digastric 



Splenius capitis 



Stylo-hyoid 



Sterno-mastoid 



Levator anguli 

 scapulae 



Scalenus anticus 



IMC. 56 '1'iiK. DKH-F.K LAYKK 01 nil-. Mr-ri.Ks 01 TMK FACE AND NKCK. 



the malar process of the superior maxilla by a strong tendon ; (2) from the 

 anterior two-thirds of the lower border of the /.ygomatic arch. From this strong 

 origin the fibres pass backward and downward to their insertion into the lower 

 half and angle of the outer surface of the ramus. (Fig. 58.) The action is to 

 draw the mandible forward. The synergist of this segment of the masseter is 

 the external pterygoid. 



The deep portion of the masseter (Fig. 56) muscle arises : (i) From the 

 inner surface of the /.ysj,omatic arch ; (2) from the lower border of the posterior 



