136 HUMAN ANATOMY. 



DEPRESSOR LABII INFERIORIS. Origin, from external ob- 

 lique line of lower jaw; insertion, into skin of lower lip, blending 

 with its fellow and the orbicularis ; action, lowers the angle of 

 the mouth ; nerve, facial. 



DEPRESSOR ANGULI ORIS. Origin, external oblique line of 

 lower jaw; insertion, into the angle of the mouth, continuous 

 with the orbicularis and risorius at its insertion and the platysma 

 at its origin ; action, depresses the angle of the mouth ; nerve, 

 facial. 



ORBICULARIS ORIS. Origin, by accessory fibres (accessorii 

 orbicularis superioris and inferioris and naso-labialis), from 

 superior and inferior maxillary borders and nasal septum ; inser- 

 tion, into the buccinator and adjoining muscles, forming the 

 sphincter of the mouth ; action, closes the lips ; nerve, facial. 



BUCCINATOR. Origin, from pterygo-maxillary ligament 

 and the posterior alveolar processes of the upper and lower jaw; 

 insertion, into orbicularis oris; action, compresses and con- 

 tracts trie cheeks; nerves, facial and buccal branch of the in- 

 ferior maxillary nerve. 



RISORIUS (SANTORINI). Origin, from fascia of masseter 

 muscle ; insertion, at angle of the mouth ; action, draws back the 

 angles of the mouth, the "smiling" muscle; nerve, facial. 



MASSETER : SUPERFICIAL PORTION. Origin, inner surface 

 of zygoma and malar process of superior maxilla; insertion, into 

 the ramus and angle of the lower jaw. 



DEEP PORTION. Origin, posterior border and inner surface 

 of the zygoma; insertion, into the ramus and coronoid process of 

 the jaw; action, raises the lower jaw, and the superficial portion 

 assists in drawing it forward ; nerve, inferior maxillary. 



TEMPORAL. Origin, from the temporal fascia and the tem- 

 poral fossa; insertion, into the coronoid process of the lower jaw ; 

 action, raises and draws backward the lower jaw; nerve, inferior 

 maxillary. 



INTERNAL PTERYGOID. Origin, from pterygoid fossa and 

 the tuberosity of the palate-bone; insertion, into the inner side 

 of the ramus and angle of the lower jaw; action, draws forward 

 and raises the lower jaw; the accessory triturating muscle of 

 mastication; nerve, inferior maxillary. 



EXTERNAL PTERYGOID. Origin, by two heads the lower 

 from the tuberosities of the palate and superior maxilla and from 

 the external pterygoid plate, the upper from the pterygoid ridge 

 on the greater wing of the sphenoid ; insertion, into the front of 

 the neck of the lower jaw and inner side of interarticular car- 

 tilage; action, draws the jaw forward; triturating muscle of 

 mastication; nerve, inferior maxillary. 



