DISSECTION OF THE HEAD AND NECK. 183 



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 pulling the external wing outwards. 



The Dilatator Naris Transversalis (Fig. 21). 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 wings 

 of the opposite sides. 



The Dilatator Naris 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. 



Action. — To dilate the false nostril. 



The Dilatator Naris Inferior. The fibres of this muscle arise 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 ascends 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 superficial portion shows a longitudinal raphe from which 

 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 



