THE HEAD AND NECK 



I20I 



inferior maxilla ; and (2) the front-of the interarticularfibro- cartilage 

 of the tempo ro -mandibular joint. 



Nerve-supply. — ^The external pterygoid nerve, which is a branch 

 of the long buccal nerve, that, in turn, being a branch of the anterior 

 portion of the inferior maxillary division of the fifth cranial nerve. 



The direction of the muscle is backwards and slightly outwards. 



Action. — (i) To draw forwards the neck and condyle of the in- 

 ferior maxilla, and also the interarticular fibro-cartilage. When 

 the muscles of opposite sides act in concert the inferior maxilla is 

 protruded, and the lower incisor and canine teeth project beyond 

 the level of those of the superior maxilla. The muscles of opposite 

 sides, however, usually act in reciprocal succession, as in the 



Long Buccal Nerve (cut) 



Upp«r Head of External Pterygoid 



Capsule of Tempore 

 mandibular Joint 



Lower Head of External 

 Pterygoid 



Pterygo-mandibular 

 Ligament 



^^i^_Stensen's Duct 



^~ Buccinator 



Internal Pterygoid 



Fig. 491. — The Pterygoid and Buccinator Muscles. 



oblique or grinding movement, the lower molars of one side being 

 carried forwards and inwards upon the corresponding upper molars, 

 and vice versa. At the same time the elevators of the inferior 

 maxilla are in action. (2) To take part in opening the mouth by 

 drawing the condyle of the inferior maxilla and interarticular fibro- 

 cartilage forwards on to the eminentia articiilaris of the temporal 

 bone. The external pterygoid is antagonistic to the posterior 

 portion of the temporal muscle. 



Relations — Superficial. — Part of the ramus of the inferior maxilla, 

 the lower part of the temporal muscle, part of the pterygoid plexus 

 of veins, the long buccal nerve, and, it may be, the second part of 

 the internal maxillary artery. Deep. — ^The upper portion of the 

 internal pterygoid muscle, the spheno-mandibular ligament, in 

 !?ome cases the second part of the internal maxillary artery, the 

 middle meningeal artery, a part of the pterygoid plexus of veins, 



76 



