INFERIOR LABIAL GROUP. 153 



and ala of the nose downwards, and diminishing the opening of the 

 nares. The levator labii superioris proprius is the proper elevator 

 of the upper lip ; acting singly, it draws the lip a little to one side. 

 The levator anguli oris lifts the angle of the mouth and draws it 

 inwards, while the zygomatici pull it upwards and outwards, as in 

 laughing. 



6. Inferior Labial Group. Depressor labii inferioris, 



Depressor anguli oris, 

 Levator labii inferioris. 



Dissection. To dissect the inferior labial region,, continue the ver- 

 tical section from the margin of the lower lip to the point of the 

 chin. Then carry an incision along the margin of the lower jaw to 

 its angle. Dissect off the integument and superficial fascia from the 

 whole of this surface, and the muscles of the inferior labial region 

 will be exposed. 



The depressor labii inferioris (quadratus menti) arises from the 

 oblique line by the side of the symphysis of the lower jaw, and pass- 

 ing upwards and inwards is inserted into the orbicularis muscle and 

 integument of the lower lip. 



Relations. By its superficial surface with a part of the depressor 

 anguli oris, and with the integument of the chin with which it is 

 closely connected. By the deep surface with the levator labii in- 

 ferioris, the labial glands and mucous membrane of the lower lip, 

 and with the mental nerve and artery. 



The depressor anguli oris (triangularis oris) is a triangular plane of 

 muscle arising by a broad base from the external oblique ridge of the 

 lower jaw, and inserted by its apex into the angle of the mouth, where 

 it is continuous with the levator anguli oris and zygomaticus major. 



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

 its deep surface with the depressor labii inferioris, the platysma my- 

 oides, the buccinator and the branches of the mental nerve and artery. 

 The levator labii inferioris (levator menti) is a small conical slip 

 of muscle arising from the incisive fossa of the lower jaw, and 

 inserted into the integument of the chin. It is in relation with the 

 mucous membrane of the mouth, with its fellow, and with the 

 depressor labii inferioris. 



Actions. The depressor labii inferioris draws the lower lip di- 

 rectly downwards, and at the same time a little outwards. The 

 depressor anguli oris, from the radiate direction of its fibres, will pull 

 the angle of the mouth either dow r nwards and inwards, or down- 

 wards and outwards, and be expressive of grief; or acting with the 

 levator anguli oris and zygomaticus major, it will draw the angle 

 of the mouth directly backwards. The levator labii inferioris raises 

 and protrudes the integument of the chin. 



7. Maxillary Group. Masseter, 



Temporalis, 

 Buccinator, 

 Pterygoideus externus, 

 Pterygoideus internus. 

 20 



