POSTERIOR MAXILLARY GROUP. 169 



Insertion. — The posterior angle and inner margin of the lower 

 jaw. 



Relation. — Externally with the parotid gland ; internally Avith 

 the guttural pouch. 



Action. — It depresses the lower jaw and draws it backwards. 



PTERYGOIDEUS INTERNUS. 



{Masseter Internus — Siyheno-maxillaris.) 



Situated on the inner surface of the lower jaw, in the maxillary 

 space, corresponding internally to the masseter, it is strong and 

 fleshy, with numerous tendinous intersections. 



Origin. — From the pterygoid process of the sphenoid bone, 

 and the palatine ridge. 



Insertion. — The inner posterior border and angle of the inferior 

 maxilla. 



Relation. — Posteriorly with the pterygoideus externus and 

 temporalis ; internally with the guttural pouch, the hyoid bone, 

 and its muscles ; externally Avith the ramus of the maxilla and 

 the inferior maxillary nerve and vessels. 



Action. — Acting with its fellow, it raises the jaw and closes 

 the mouth ; when acting singly, it produces lateral motion. 



PTERYGOIDEUS EXTERNUS. 



[Part of Spheno-maxillaris.) 



Situated behind the preceding, on the front and inner side of 

 the temporo-maxillary articulation, it is short, thick, and fleshy, 

 with slight tendinous intersections. 



Origin. — From the ala and pterygoid process of the sphenoid 

 bone. 



Insertion. — Passing backwards and downwards, it reaches a 

 roughened depression on the inner side of the inferior maxilla, just 

 below its condyle. 



Relation. — With the temporalis and the pterygoideus inter- 

 nus, which is below and before it. 



Action. — It assists the internus, and also draws the lower jaw 

 forwards, antagonising the stylo-maxillaris. 



