POSTERIOR MAXILLARY GROUP. 



167 



Action. — It compresses the upper lip, and perhaps assists in 

 •dilating the nostril. 



LEVATOR LABII INFERIORIS. 

 (Levator Menti.) 



Situated on the inner surface of the under lip, below the 

 lucous membrane, it is like the preceding in shape. 



Origin. — From the alveoli of the inferior maxilla, between the 

 lateral incisors and tushes. 



Insertion. — The under lip by diverging fibres. 



Action. — It elevates the under lip and chin, and presses the 

 [lip on the teeth. 



DEPRESSOR LABII INFERIORIS. 



{Maxillo-lahialis. ) 



(Pl. II. 10. Fig. 70. h.) 



Situated along the surface of the lower jaw, it is in shape long 

 ftind pyramidal. 



Origin. — Posteriorly, in common with the buccinator, from 

 the alveolar tuberosity, and the superior border of the inferioi 

 maxilla, behind the molar alveoli. 



Insertion. — The infero-lateral part of the under lip by a flat 

 itendon. 



Action.* — To depress the under lip. 



Posterior Maxillary Group. 



The muscles constituting this group are chiefly those of. masti- 

 •cation, which act upon the temporo-maxillary joint. They are as 

 follows : 



Masseter. 



Temporalis. 



Stylo-inaxillaris. 



Pterygoideus intemus. 

 Pterygoideus extemus. 

 Digastricus. 



* [While dissecting at the Edinburgh Veterinary College in December, 1868, 

 I was particularly struck with the action of this muscle ; its tendon subdivides 

 in the areolar and muscular tissue of chin and posterior lip, and its action is 

 not quite to depress the under lip, but to elevate the chin and lower lip, and 

 thus separate the lower lip from the lower incisors. This is the opinion, I find, 

 Tecorded by the late Professor Goodsir in his posthumous manuscript. — Ed., 

 First Edition.] 



