178 THE ANATOMY OF THE HOESB. 



labii superioris proprius ; and widening as it descends, it divides into 

 an anterior and a posterior branch, between which the lateral dilator of 

 the nostril emerges. The anterior is the larger branch, and it passes 

 beneath the last-mentioned muscle to end. in the outer wing of the 

 nostril and the adjacent part of the upper lip. The posterior branch is 

 inserted into the angle of the mouth. 



Action. — To dilate the nostril and elevate the upper lip by its 

 anterior branch ; to raise the angle of the mouth by its posterior 

 branch. 



The Levator Labii Supebioris Propeids (Plates 29 and 30, and fig. 

 19). By its superior extremity, which is rounded and fleshy, this 

 muscle takes origin below the orbit, from the malar and superior maxil- 

 lary bones. Becoming narrower and thicker, it passes downwards and 

 forwards beneath the last-described muscle, whose direction it crosses. 

 Appearing in front of this muscle, it lies on the false nostril ; and here its 

 muscular portion is succeeded by a narrow tendon, which passes inwards 

 above the superior commissure of the nostril to gain the upper lip. In 

 the lip it passes over the transverse dilator of the nose ; ■ and approach- 

 ing the muscle of the opposite side, it becomes united to it across the 

 middle line by an intermediate fascia, and is inserted into the texture of 

 the upper lip. 



Action. — Acting together, the right and left muscles elevate the 

 upper lip vertically. When the muscle of either side acts singly, the 

 lip is raised and inclined towards that side. 



The Dilatator Naris Lateralis. (Doubtfully the homologue of 

 the caninns of man) (Plate 29). This muscle, is triangular in form. 

 It is narrow and pointed at 'its upper extremity, where it arises from 

 the superior maxilla. It passes between the two branches of the levator 

 labii superioris alseque nasi ; and widening as it descends, it passes over 

 the anterior branch of that muscle, and becomes inserted into the outer 

 wing of the nostril. Its most posterior fibres blend with the orbicularis 

 oris. 



Action. — To dilate the nostril by j)ulling the external wing outwards. 



The Dilatator Naris Teansversalis (Fig. 19). This is a four-sided, 

 fleshy muscle, whose fibres pass transversely across the middle line, and 

 are inserted at either extremity into the broad part of the comma-like 

 cartilage of the nostril. It is partly covered by the termination of the 

 levator labii superioris proprius. 



Action. — To dilate the nostrils by approximating the internal wino-s of 

 opposite sides. 



The Dilatator Naeis Superior. This muscle comprises a few pale 

 fasciculi which arise from the projecting edge of the septum nasi at the 

 side of the nasal peak, and terminate in the wall of the false nostril and 

 on the extremity of the ethmoidal (anterior) turbinated bone. 



