POSTERIOR MAXILLARY GROUP. 169 



Insertion. The posterior angle and inner margin of the lower 

 jaw. 



Relation. Externally with the parotid gland ; internally with 

 the guttural pouch. 



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



PTERYGOIDEUS INTERNUS. 

 (Jlasseter Intemus Spheno-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 with 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. 



