DISSECTION OF THE HEAD AND NECK. 185 



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 anas- 

 tomose 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 papilla? 

 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 to a musclefof the 

 lower lip resembling the depressor already dissected in the upper. Its 

 fibres arise on each side from the inferior maxilla beneath the inter- 

 mediate 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 Masseter (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 

 and tendinous, but posteriorly it is fleshy. Other strong tendinous 

 layers are included within the substance of the muscle, and give 

 attachment to many of its fasciculi. The muscle arises from the 

 zygomatic ridge of the malar and superior maxillary bones, and it 

 becomes inserted into the outer surface of the vertical ramus. 



Action. — To elevate the lower jaw, and aid in mastication by bringing 

 the lower teeth forcibly into contact with the upper. 



The Submaxillary or Facial Artery has already been dissected in 

 the intermaxillary space. It reaches the face by turning round the 

 edge of the inferior maxilla, in company with the vein of the same 

 name and Stenson's duct (Plate 29). Here the artery is the most 

 inferior of the three vessels, and the duct is the most superior. The 

 three vessels cross the inferior maxilla at the lower edge of the masseter 

 muscle, and preserve the before-mentioned relationship until they pass- 

 on to the buccinator. Here the vessels cross over the duct, being 

 themselves crossed superficially by the facial nerves ; and, passing- 

 beneath the zygomaticus, below the zygomatic spine, they reach the 

 surface of the superior maxilla, on which the artery divides into an 

 angular and a nasal branch. The angular branch detaches «a twig to 

 anastomose with the orbital branch of the superior dental artery, and is 

 then distributed to the muscles and skin beneath the orbit. The nasal 

 branch reaches the false nostril by passing beneath the levator labii 

 superioris alseque nasi. The collateral branches which the submaxillary 



