164 MYOLOGY. 



Action. — It retracts the angle of the mouth, but specially 

 serves to force the food between the molars, and to prevent the 

 buccal membrane from being injured by the latter. 



ORBICULARIS ORIS. 



{Labialis.) 



(PL. IL 8.) 



This is a sphincter or annular constrictor muscle, and as such 



has virtually neither origin nor insertion ; surrounding the mouth 



and forming the substance of the lips, it is separable into two 



layers, and is related internally with the mucous membrane of 



the mouth and the labial glands, and externally with the skin, 



to which it is firmly adherent. It is the intrinsic muscle of the 



lips, and receives for the most part the insertions of the extrinsic 



muscles. 



Action. — It is the constrictor of the anterior aperture of the 

 mouth, and also assists in mastication, suction, and prehension of 

 food. 



LEVATOR LABII SUPERIORIS AL^QUE NASL 

 (Sitpernaso-lahialis.) 

 (Pl. IL 6.) 

 Situated superiorly, on the side of the cheek, running forwards 

 and downwards, this muscle is long, flat, and aponeurotic supe- 

 riorly, dividing into two unequal bands, between which passes the 

 dilatator naris lateralis. 



Origin. — It arises from the frontal and nasal bones, the 

 anterior division, the larger and thicker, passing under the dila- 

 tator above named. 



Insertion. — To the nostril and upper lip, the posterior division 

 reaching the angle of the mouth. 



Action. — It raises the upper lip and angle of the mouth, and 

 dilates the nostril. 



NASALIS LONGUS. 

 {SupermaxiUo-Iahialis.) 

 (Pl. II. 4. Fig. 70. cj.) 

 Situated below the preceding muscle, this muscle runs hori- 

 zontally forwards. In shape it is pyramidal, with a fleshy belly 

 and a long tendon of insertion. 



