International Medical And Surgical Survey 1922

Excerpt from International Medical and Surgical Survey, 1922, Vol. 4 Worthmann endeavored to determine whether the dense, ivory-like texture of the petrosa is ascribable merely to its function as the rein forcing rib of the cranial vault or also to its participation in the func tion of the temporomandibular articulation. For this purpose he studied the cranium in predatory animals as these are destitute of the external pterygoid muscle, and the temporomandibular articulation has the move ment of a simple hinge joint. The muscles of mastication are divisible into 2 groups according to the direction of their pull: (1) an anterior one, consisting of the internal pterygoid and masseter, which transmits the pressure only to the facial skeleton, and (2) a posterior group, represented by the temporal muscle, which transmits it also to the cranium. The action of each muscle may be represented by a single straight line connecting the centers of the surfaces of origin and insertion. In the case of the first 2 muscles, this axis falls vertically on the center of the line connecting the temporomandibular articulation with the contact surface of the last pair of molars; in the case of the temporal muscle, it falls obliquely on the prolongation of this line within the dental arches. Resolved into its components, the one acting in the direction of the temporomandibular articulation is greater than that of mastication pressure. Articular pressure is offset by reinforcements in the skull to which the petrosa belongs. As the temporal muscle is the only muscle transmitting maxillary power to the cranium and thence to the cervical musculature, it is developed most strongly in those animals who are compelled to carry great weights between the maxillas. In man the action of the internal pterygoid serves to compensate for the underdevelopment of the coronoid process and its unfavorable influence on the utilization of the temporal muscle's power with opened mouth, to keep the articular component of the temporal muscle's pressure from the cranium, and to render possible the isolated action of the incisors in biting. About the Publisher Forgotten Books publishes hundreds of thousands of rare and classic books. Find more at www.forgottenbooks.com This book is a reproduction of an important historical work. Forgotten Books uses state-of-the-art technology to digitally reconstruct the work, preserving the original format whilst repairing imperfections present in the aged copy. In rare cases, an imperfection in the original, such as a blemish or missing page, may be replicated in our edition. We do, however, repair the vast majority of imperfections successfully; any imperfections that remain are intentionally left to preserve the state of such historical works.

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