MUSCLES OF THE MOUTH. 555 



mouth, the depressors of the lower lip and of the angle of the mouth, 

 the zygomatic and risorius muscles, and a wide muscle of the cheek 

 closing the space between the jaws (the buccinator). Lastly, an 

 orbicular muscle surrounds the opening, but it is largely composed 

 of fibres of the preceding muscles. 



The LEVATOR LABII SUPERIORIS extends vertically from the Elevator of 

 lower margin of the orbit to the orbicularis oris. It arises from 

 l he upper maxilla above the infraorbital foramen and from the 

 innermost part of the malar bone, and is inserted into the skin 

 of the upper lip, its fibres interlacing with those of the orbicularis. 

 Xear the orbit the muscle is overlapped by the orbicularis palpe- 

 brarum, but below that spot it is subcutaneous. By its inner side relations : 

 it joins the common elevator of the ala of the nose and upper lip ; 

 and to its outer side lie the zygomatic muscles, the small one 

 joining it. Beneath it are the infraorbital vessels and nerve. 



Action. By the action of this muscle the upper lip is raised, use. 

 and the skin of the cheek is bulged below the eye. 



The DEPRESSOR LABII iNFERiORis is opposite the elevator of the 

 upper lip, and has much yellow fat mixed with its fibres. The 

 muscle has a wide origin from a depression on the front of the 

 lower jaw, reaching from near the symphysis to a little beyond the 

 mental foramen ; ascending thence it is inserted into the skin of the 

 lower lip. Its inner border joins in the lip the muscle of the oppo- 

 site side ; and its outer is overlapped by the depressor anguli oris. 



Action. If one muscle contracts, the half of the lip of the same use 

 side is depressed and everted ; but by the use of both muscles, the 

 whole lip is lowered and turned outwards, and rendered tense at 

 the centre. 



The LEVATOR AXGULI ORIS has well-marked fibres, and is partly Elevator of 

 concealed by the levator labii superioris. Arising from the canine * 

 fossa of the upper jaw below the infraorbital foramen, its fibres 

 descend towards the angle of the mouth, where they are superficial to 

 the buccinator and are partly inserted into the skin, but the greater enters orbi- 

 number are continued into the orbicularis of the lower lip, and sweep 

 round below the mouth to the opposite side of the middle line. 



Action. This muscle elevates the corner of the mouth, and acts use. 

 as an antagonist to the depressor. 



The DEPRESSOR ANGULI ORIS is triangular in shape. It arises from Depressor 

 the oblique line on the outer surface of the lower jaw ; and ascending 

 to the angle of the mouth, a few of its fibres are there inserted into 

 the skin, but the greater number decussate with those of the also joins 

 elevator muscle and pass into the upper part of the orbicularis, and r 

 sweep round above the mouth to the opposite side of the middle 

 line. The depressor conceals the mental branches of the inferior 

 dental vessels and nerve. It is united at its origin with the 

 platysma myoiiles, and near its insertion with the risorius muscle. 



Action. The angle of the mouth is drawn downwards by it, as use. 

 is exemplified in a sorrowful countenance. 



The ZYGOMATIC MUSCLES are directed obliquely from the malar Zygomatic 

 bone towards the angle of the mouth and the upper lip. One is lllu * cles ' 



