180 THE ANATOMY OF THE HOBSE. 



having either origin or insertion, its fibres forming a continuous ellipse. 

 In both lips the fibres are intimately adherent to the skin, and they are 

 partially blended with the labial insertions of some of the muscles 

 already dissected. 



Action. — To approximate the lips, as in the simple act of closing the 

 mouth or in prehension. 



Directions. — Evert the upper lip, and wipe its exposed mucous lining 

 clean. Observe that it is studded with numerous short, tubercle-like 

 papillfB. Each of these is perforated by the duct of a labial mucous 

 gland lying beneath the mucous membrane. Now dissect away the 

 mucous membrane so as to expose these glands. At the same time, 

 there will be brought into view the following muscle : — 



The Depkessoe Labii Superioris. Under this name, Percivall 

 describes a bundle of muscular fibres that in the human subject is 

 reckoned a part of the buccinator. On each side the muscle arises from 

 the premaxillary bone above the corner incisor and the interdental 

 space as far as the canine tooth ; and, on the other hand, its fibres 

 terminate in the upjjer lip, blending with the orbicularis. Branches of 

 the infra-orbital and 7th nerves enter the lip between the outer edge 

 of this muscle and the lowest fibres of the buccinator. 



Action. — To assist the orbicularis by depressing the upper lip. 



The Palato-Labial Artery. While the upper lip is kept everted, 

 dissect backwards on the middle line imtil this artery is found coming 

 forwards from the roof of the mouth by the incisor foramen. At its 

 point of exit it bifurcates, its branches passing right and left to anasto- 

 mose with the superior labial artery. 



Directions. — Evert the lower lip, and wipe its mucous surface clean. 

 Notice that it is smooth, with few or none of the tubercle-like papillae 

 found on the upper lip. Dissect away the mucous membrane, which is 

 intimately adherent to the orbicularis muscle. There are few or no 

 labial mucous glands in the lower lip. 



The Levator Menti. This is the name given by Percivall to a 

 muscle of the lower lip resembling the depressor already dissected in the 

 upper. Its fibres arise on each side from the inferior maxilla beneath 

 the intermediate and corner incisors, and from the interdental space as 

 far as the canine tooth. It runs downwards and backwards to terminate- 

 in the so-called prominence of the chin, being there intermixed with 

 fibrous tissue, and confounded in front with the orbicularis oris. The 

 inferior labial artery enters the lip between the outer edge of the muscle 

 and the lower fibres of the buccinator. 

 Action. — To elevate the lower lip. 



The Massetbh (Plate 29). This muscle covers the vertical ramus of 

 the lower jaw. It has a flattened, semicircular form, and is thick and 

 powerful. In its anterior half the surface of the muscle is glistening 



