DISSECTION OP THE HEAD AND NECK. 181 



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 sxirfiice of the vertical rami;s. 



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

 tlie lower teeth forcibly into contact with the iipper. 



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 dvict is the most superioi'. 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 

 ancjular 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 

 gives off in this part of its course are the superior and inferior labial 

 arteries ; and unnamed cutaneous or muscular branches, of which 

 those that pass to the masseter muscle are the largest. 



The Inferior Labial Artery is the largest branch. It is given off on 

 the surface of the inferior maxilla. It passes beneath the depressor 

 labii inferioris, and descends to the lower lip, at the hinder edge of the 

 buccinator. At the mental foramen it anastomoses with the mental 

 branch of the inferior dental artery, and in the lip it anastomoses on 

 the mesial plane with the opposite vessel. 



The Superior Labial Artery is detached opposite the zygomatic ridge. 

 It passes beneath the levator labii superioris alfcque nasi and the lateral 

 dilator of the nostril, and reaches the upper lip, in which it anastomoses 

 with the palato-labial artery. 



The Submaxillary Vein (Plate 29) runs in close company with the 

 artery. Where the vessels appear on the face, and throughout the 

 greater part of their course, the vein is above the artery. It is formed 

 by an angular and a nasal branch, the first of which begins in the lower 

 eyelid, while the other originates beneath the skin of the false nostril, 

 and passes over the levator labii superioris alreque nasi to join the first. 

 It receives branches corresponding to those of the artery, and, in addi- 

 tion, the alveolar and buccal veins join it at the edge of the masseter. 



