DISSECTION OF THE HEAD AND NECK. 179 



Action. — To dilate the fixlse nostril. 



The Dilatator Naris Inferior. The fibres of this muscle caise from 

 the free edge of the premaxillary and superior maxillary bones ; and 

 they terminate in the wall of the false nostril, and on the cartilaginous 

 prolongation of the maxillary' (posterior) turbinated bone. 



Action. — The same as the preceding muscle. 



The Zygomaticus (Plate 29) is a riband-shaped muscle, often 

 extremely thin. It extends vertically between its point of origin from 

 the surface of the masseter, behind the lower portion of the zygomatic 

 ridge, and its insertion into the buccinator above the angle of the mouth. 



Action. — To raise the angle of the mouth. 



The Buccinator (Plate 29). This muscle forms the main mass of 

 the cheek. It is not wholly exposed at present, its upper extremity 

 being covered by the masseter. It comprises a superficial and a deep 

 portion, the former being separately described by Percivall as the 

 caninus. The supei-ficial portion shows a longitudinal rcqihe from wdiich 

 the muscular fibres pass forwards and backwards in a penniform manner. 

 In front these fibres become attached to the superior maxilla, from the 

 alveolus for the canine tooth to that for the first molar inclusive ; and 

 behind, to the inferior maxilla opposite the interdental space between 

 the canine and the first molar. The deep portion of the muscle is 

 longer but narrower than the preceding. It arises from the superior 

 maxilla in front of the three upper molar alveoli ; from the scabrous 

 imprint on the same bone above the last alveolus ; and from the edge 

 of the inferior maxilla above the last alveolus. Inferiorly the fibres of 

 the muscle blend with the orbicularis oris at the angle of the mouth. 

 As will be seen at a later stage, after the removal of the masseter, the 

 superior buccal gland lies on the muscle at its anterior edge, while the 

 inferior buccal gland lies under its posterior edge, and the mucous 

 membrane of the mouth lines its inner surface. 



Action. — When unopposed by the orbicularis oris, the muscle will 

 retract (elevate) the angle of the mouth ; but otherwise, as in mastica- 

 tion, it compresses the cheek against the teeth and their alveoli, and 

 tends to keep the food between the xipper and the lower molars. In 

 man, when the cheeks are distended, as in blowing a wind instrument, 

 the muscle compresses the volume of air and propels it as a stream 

 from the mouth : hence the name, from the L. huccina, a trumpet. 



The Depressor Labii Infbrioris (Plate 29). This muscle is placed 

 along the hinder edge of the buccinator, with which it is confounded at 

 its origin from the alveolar edge of the inferior maxilla above the last 

 molar tooth. It terminates in the texture of the lower lip. 



Action. — To depress (retract) the lower lip. 



The Orbicularis Oris (Plate 29). This muscle surrounds the 

 .aperture of the mouth like a sphincter. It cannot be described as 



