THE MUSCLES OF THE HEAD AND NECK 131 



which are not distinct, but fuse with the muscles in- 

 serted into the skin and mucous membrane surround- 

 ing the mouth. The buccinator muscle divides at the 

 angle, and the fibers pass into the upper and lower 

 part of the orbicularis oris; also at the angle entering 

 from above are the fibers of the levator anguli oris, 

 and from below the fibers of the depressor anguli oris. 

 In addition to the former muscles crossing at the angle, 

 are the fibers of the risorius which divide and blend 

 with the upper and lower lips respectively. The other 

 muscles inserted into the lips are: above, levator labii 

 superioris (elevator of upper lip); levator labii supe- 

 rioris alaeque nasi (elevator of the upper lip and wing 

 of the nose); the zygomaticus major and minor; and 

 depressor labii inferioris (depressor of the lower lip). 

 Actions are numerous and various, and only the ordi- 

 nary or chief actions will be mentioned, as the muscles 

 inserted into the orbicularis oris all aid it in the com- 

 plex movements of this important muscle of expression. 

 When the fibers contract they close the lips; the crossed 

 fibers consisting of the superficial set brings the lips 

 together and also protrudes them as in whistling, 

 pouting, etc., the deep fibers assisted by the oblique 

 fibers forcibly close the lips and hold them against the 

 teeth as when one refuses to take food or medicine 

 by mouth. 



Nerve facial. 



Buccinator. This is the chief muscle of the cheek, 

 and encloses the space between the two jaw bones. 

 It is thus quadrilateral in shape. Arises from the alve- 

 olar processes of the maxillae and mandible, behind from 

 a thickened fibrous band, called the pterygomandibular 

 ligament. The fibers come together at the angle of the 

 mouth and pass to the upper and lower lips. Action 

 it is essentially a muscle of mastication. The muscle 

 contracts the cheeks and compresses them so that the 

 food during mastication is kept within the bounds of 

 the teeth and comes in contact with their chewing 



