MAXILLARY REGIONS. 247 



he upper lip and ala of the nose ; its most important action is upon the nose, 

 which it dilates to a considerable extent. The action of this muscle produces a 

 marked influence over the countenance, and is the principal agent in the expression 

 of contempt. The two Dilatores nasi enlarge the aperture of the. nose, and the 

 Compressor naris appears to act as a dilator of the nose rather than as a constrictor. 

 The Depressor alas nasi is a direct antagonist of the preceding muscles, drawing 

 the ala of the nose downwards, and thereby constricting the aperture of the nares. 



6. SUPERIOR MAXILLARY REGION (fig. 148). 



Levator Labii Superioris. Zygomaticus major. 



Levator Anguli Oris. Zygomaticus minor. 



The Levator Labii Superioris is a thin muscle of a quadrilateral form. It 

 arises from the lower margin of the orbit immediately above the infra-orbital 

 foramen, some of its fibres being attached to the superior maxilla, some to the 

 malar bone ; its fibres converge to be inserted into the muscular substance of the 

 upper lip. 



Relations. By its superficial surface, with the lower segment of the Orbicu- 

 laris palpebrarum; below, it is subcutaneous. By its deep surface, it conceals 

 the origin of the Compressor naris and Levator anguli oris muscles, and the infra- 

 orbital vessels and nerves, as they escape from the infra-orbital foramen. 



The Levator Anguli Oris arises from the canine fossa, immediately below the 

 infra-orbital foramen ; its fibres incline downwards and a little outwards, to be 

 inserted into the angle of the mouth, and intermingle with those of the Zygo- 

 matici, the. Depressor anguli oris, and the Orbicularis. 



Relations. By its superficial surface, with the Levator labii Superioris and the 

 infra-orbital vessels and nerves. By its deep surface, with the superior maxilla, 

 the Buccinator, and the mucous membrane. 



The Zygomaticus major is a slender fasciculus, which arises from the malar 

 bone, in front of the zygomatic suture, and, descending obliquely downwards and 

 inwards, is inserted into the angle of the mouth, where it blends with the fibres 

 of the Orbicularis and Depressor anguli oris. 



Relations. By its superficial surface, with the subcutaneous adipose tissue. 

 By its deep surface, with the malar bone, the Masseter and Buccinator muscles. 



The Zygomaticus minor arises from the malar bone, immediately behind the 

 maxillary suture, and, passing downwards and inwards, is continuous with the 

 outer margin of the Levator labii superioris. It lies in front of the preceding. 



Relations. By its superficial surface, with the integument and the Orbicularis 

 palpebrarum above. By its deep surface, with the Levator anguli oris. 



Nerves. This group of muscles is supplied by the facial nerve. 



Actions. The Levator labii superioris is the proper elevator of the upper lip, 

 carrying it at the same time a little outwards. The Levator anguli oris raises the 

 angle of the mouth and draws it inwards ; whilst the Zygomatici raise the upper 

 lip and draw it somewhat outwards, as in laughing. 



7. INFERIOR MAXILLARY REGION (fig. 148). 



Levator Labii Inferioris or Levator menti. 

 Depressor Labii Inferioris or Quadratus menti. 

 Depressor Anguli Oris or Triangularis menti. 



Dissection. The Muscles in this region maybe dissected by making a vertical incision through 

 the integument from the margin of the lower lip to the chin : a second incision should then be 

 carried along the margin of the lower jaw as far as the angle, and the integument carefully 

 removed in the direction shown in fig. 147. 



The Levator Labii Inferioris or Levator menti is to be dissected by everting the 

 lower lip and raising the mucous membrane. It is a small conical fasciculus. 



