Dental review; devoted to the advancement of dentistry. . r side of the jaws ; and the externaland internal pterygoids, attached to its inner sides. The masseter, temporal and internal pterygoid muscles closethe jaw and press the teeth against one another, and this is theirprincipal action. They are antagonized by the digastric, the mylo-hyoid and geniohyoid muscles, which, aided perhaps by the platysma, t Tomes Dental Anatomy, p. 557. 850 THE DENTAL REVIEW depress the lower jaw when the hyoid bone is fixed by its owndepressor muscles. The external pterygoid draws the jaw forward, and so, in s
Dental review; devoted to the advancement of dentistry. . r side of the jaws ; and the externaland internal pterygoids, attached to its inner sides. The masseter, temporal and internal pterygoid muscles closethe jaw and press the teeth against one another, and this is theirprincipal action. They are antagonized by the digastric, the mylo-hyoid and geniohyoid muscles, which, aided perhaps by the platysma, t Tomes Dental Anatomy, p. 557. 850 THE DENTAL REVIEW depress the lower jaw when the hyoid bone is fixed by its owndepressor muscles. The external pterygoid draws the jaw forward, and so, in somemeasure, tends to open it; as the two muscles do not always, or,indeed, generally, act together, they give a lateral movement to thejaw. The superficial portions of the masseter and the internalpterygoid are ordinarily supposed, as their direction is slightlybackward, to assist in drawing the jaw forward; but Langer, arecent investigator of their action, attaches very little importance tothis, and, indeed, considers that, when the jaw has been pulled. Fig. 9. forward by the external pterygoid, the combined action of theinternal pterygoid, the temporal and the masseter may bring it backagain. . The position of repose is neither complete closure nor openingof the jaws; in persons with enlarged tonsils the habitual positionis one with the mouth somewhat more widely open, owing to thedifficulty in breathing through the nose.* I have found the resistance necessary to retain the lower jaw5 mm. in a forward pose, when all the muscles are relaxed, variesfrom 30 to 60 grams. This amount, though comparatively small, *Dental Anatomy, Tomes. 0R1GIXAL CGMMUNICA TIOXS. 851 is sufficiently great to render it absolutely impossible for the externalpterygoid to hold the jaw in a fixed forward position. The natural tendency of the muscles is to retain the condylesin their natural position in the glenoid fossae. The incline plane ofthe Kingsley plate, when the jaw is in repose, offers no resist
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