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MASTICATION AND DEGLUTITION. 



mylq-hyoidei muscles, draws the lower jaw down, when we open 

 the mouth. 



" The masseters and temporal chiefly raise it again when we 

 bite off any thing, and are most powerfully contracted when we 

 break hard substances. , . ,. .. 



" Its lateral motions are accomplished by the internal and ex- 

 ternal pterygoid. 

 - " The latter can also draw it forwards. 



" Substances are retained, directed, and brought under the 

 action of the teeth, by the buccinator, and by the tongue, which 

 is very flexible and changeable in form. 



a, temporal muscle, inserted by a tendon 

 into the coronoid process of the lower jaw : 

 6, masseter arising from the zygoma, and 

 inserted into the angle of the lower jaw : 

 c, buccinator, or great muscle of the cheek, 

 the action of which is to lessen the cavity of 

 the mouth, and draw the angle of the lips 

 backwards. The mere inspection of the 

 other muscles shows their action, d, the 

 parotid gland : e, its duct : /, a portion of 

 the sub-maxillary gland uniting with the 

 parotid. 



a, external pterygoid, arising from the 

 pterygoid process and zygomato-temporal sur- 

 face of the sphenoid bone, and the tuberosity 

 of the os palati, and inserted into the front of 

 the neck of the condyle of the lower jaw, and 

 interarticular cartilage. b, internal pterygoid, 

 arising from the pterygoid fossa of the sphe- 

 noid bone, and from the pterygoid processes 

 of the palate bone, and inserted within the 

 angle of the lower jaw. 



