. The anatomical record. Anatomy; Anatomy. 366 FKEDERIC POMEROY LORD the stylomandibular ligament in its function of helping main- tain a transverse axis of rotation for the mandible when the mouth is opened? At least it suggests a reason, when otherwise none is given, for the persistence of that portion of the first vis- ceral arch. This model, to recapitulate, demonstrates the following:. Fig. 5 Diagram to show relation between lines of force of the muscles, which forcibly open, and which close, the mouth. The two lines meeting at 0 represent the direction of pull of the external pterygoid a
. The anatomical record. Anatomy; Anatomy. 366 FKEDERIC POMEROY LORD the stylomandibular ligament in its function of helping main- tain a transverse axis of rotation for the mandible when the mouth is opened? At least it suggests a reason, when otherwise none is given, for the persistence of that portion of the first vis- ceral arch. This model, to recapitulate, demonstrates the following:. Fig. 5 Diagram to show relation between lines of force of the muscles, which forcibly open, and which close, the mouth. The two lines meeting at 0 represent the direction of pull of the external pterygoid and digastric muscles, used in forcible opening; those meeting at C represent the direction of pull of the masseter (the fibers of the internal pterygoid, so far as closing the mouth is concerned, are practically parallel with those of the masseter) and the posterior fibers of the temporal, used in closing the mouth. In both cases it is apparent that the mandible will rotate about a point near the attachment of the stylo-mandib- ular ligament. First. That the jaw is depressed in ordinary opening of the mouth by the unassisted action of the two external pterygoid muscles, which pull the menisci and condyles forward, make taut the stylo-mandibular, and probably the spheno-mandibular, liga- ments, and then rotate the mandible about a transverse axis drawn through the insertion of the ligaments. Second. That, in forcible depression of the mandible, the di- gastrics assist by preventing too great tension on the stylo-man-. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Bardeen, Charles Russell, 1871-1935, ed; Boyden, Edward A. (Edward Allen), 1886-1976; Bremer, John Lewis, 1874- ed; Hardesty, Irving, b. 1866, ed; American Association of Anatomists; American Society of Zoologists; Wistar Institute of Anatomy and B
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