1170 A MANUAL OF ANATOMY 



of the mouth it becomes narrow and thick. It is pierced by 

 Stensen's duct opposite the second upper molar tooth, and the 

 long buccal nerve also passes through it on its way to the mucous 

 membrane of tUe cheek. Externally the muscle is overlapped by 

 the anterior border of the masseter, from which it is separated by 

 the buccal pad of fat. 



Buccal Pad of Fat. — ^This is a well-defined collection of fat which 

 is situated upon the buccinator muscle close to the anterior border 

 of the masseter. It is continuous with the fat of the zygomatic 

 fossa, and is well developed in young children. 



Depressor Anguli Oris {triangularis menti) — Origin. — ^The external 

 oblique line of the inferior maxilla, from about the level of the 

 canine alveolus to about the level of the first molar alveolus. 



Insertion. — ^The angle of the mouth, where some of the fibres 

 are attached to the skin, whilst others decussate with those of the 

 levator anguli oris and enter the upper lip, in which they mingle 

 with the upper part of the orbicularis oris. 



Nerve-supply. — The facial nerve. 



Action. — ^To depress the angle of the mouth. 



Internally the muscle overlaps a portion of the depressor labii 

 inferioris. 



Depressor Labii Inferioris {quadratus menti) — Origin. — ^The lower 

 part of the outer surface of the body of the inferior maxilla, com- 

 mencing almost close to the symphysis, and extending outwards to 

 a point just below the mental foramen. 



Insertion. — ^The skin of the lower lip. 



Nerve-supply. — ^The facial nerve. 



The muscle is directed upwards and inwards. 



Action. — ^To draw the lower lip downwards and slightly outwards. 



The muscle is overlapped externally by a portion of the depressor 

 anguli oris, and internally it is in contact superiorly with its fellow 

 of the opposite side. The deep surface is related externally to the 

 mental foramen and the mental nerve and vessels, and internally 

 to part of the levator menti. In the lower lip its fibres pass amongst 

 those of the lower part of the orbicularis oris. 



Levator Menti, or Levator Labii Inferioris — Origin. — ^The incisor 

 fossa of the inferior maxilla. 



Insertion. — ^The skin of the chin. 



Nerve-supply. — ^The facial nerve. 



The muscle is directed downwards and forwards. 



Action. — (i) To raise the integument of the chin ; and (2) to elevate 

 and protrude the lower lip. It gives rise to a proud or imperious 

 expression, and has been hence called the musculus superbus. 



Superiorly the muscle is under cover of the depressor labii in- 

 ferioris. Interiorly it appears along with its fellow, between the 

 two depressor labii inferioris muscles. 



Orbicularis Oris. — This is a complex muscle, being composed of 

 three strata. The superficial stratum consists of fibres which are 

 prolonged from the elevators and depressors of the angles of the 



