THE MUSCULAR SYSTEM 59 



as they are able to alter the shape of the mouth so that 

 various expressions may be assumed. 



Inferior Maxillary Region. Here we have the ' 

 levator labii inferioris, depressor labii inferioris, depressor 

 anguli oris. Action of the levator labii is to raise the lower 

 lip; it also protrudes it, and at the same time wrinkles 

 the chin. The depressor labii inferioris draws the lip 

 downward and outward. The depressor anguli oris 

 draws the angle of the mouth directly backward. These 

 muscles all blend with other muscles of the face (Fig. 31). 



Intermaxillary Region. Contains the orbicularis 

 oris, buccinator, and risorius. The orbicularis oris is a 

 sphincter muscle, elliptic in form, and surrounds the oral 

 aperture (mouth); it unites with the buccinator on each 

 side, as well as with the several muscles of the face. 

 Action, closes the lips. 



The buccinator is a broad, thin muscle. Action, assists 

 in the process of mastication; compresses the cheeks, so 

 that the food is kept in immediate contact with the 

 teeth. 



The risorius has its insertion in the angle of the mouth. 

 Action, draws out the angle of the mouth and compresses 

 the cheek. 



Temporomaxillary Region. The two muscles in 

 this region are of great importance; they are named the 

 masse ter and the temporal. The masseter is a short, 

 thick muscle, consisting of two portions-^superficial and 

 deep. It arises from the malar process of the superior 

 maxilla and zygomatic arch, and is inserted into the 

 angle of the lower jaw. Action, a muscle of masti- 

 cation. 



The temporal is a broad muscle, situated on the side of 

 the head, arising from temporal fossa and fascia, and in- 

 serted in the coronoid process of the inferior maxillary 

 bone. Action, assists in the process of mastication. 



