The laws and mechanics of circulation, with the principle involved in animal movement . emporals in-crease the action for divaricating and closing the jaws. Such, in brief, is the tremendous force for closing the jawsby contraction, while there are no opposing muscles for open-ing it by contraction, the small floating muscles in the infra-maxillary region already referred to, with the hyoid bonefixed by means of the long, slender muscles (sterno-hyoid,sterno-thyroid, and omo-hyoid) connected with the sternum andscapulae, may have some influence in opening the mouth,but that they are not import
The laws and mechanics of circulation, with the principle involved in animal movement . emporals in-crease the action for divaricating and closing the jaws. Such, in brief, is the tremendous force for closing the jawsby contraction, while there are no opposing muscles for open-ing it by contraction, the small floating muscles in the infra-maxillary region already referred to, with the hyoid bonefixed by means of the long, slender muscles (sterno-hyoid,sterno-thyroid, and omo-hyoid) connected with the sternum andscapulae, may have some influence in opening the mouth,but that they are not important muscles in this respect, is nowfully proven to demonstration. The mouth is opened withgreat energy and celerity—opened as quickly as it is closed,and with considerable force. In proof of this latter circum- DUALISM DEMONSTRATED. 473 stance, let the student place his hand under the jaw with theobject of arresting the action, and he will be at once convinced;he will also produce pain at the head of the bone from strainto the ligaments, produced by the action of the muscles tend-. Fig. 196.—Excision of the Zygomatic Arch, showing attachment of the temporal muscle(2); in the coronoid process (1); reduced.—Bougery, ebc. ing to force it downward and backward, the anterior portionsbeing immovable. Furthermore, he will find by palpatingthe masseters that there is increasing hardness, or the same aswith divarication in the jaw, and when fully opened the mus-cles seem as hard as iron, from afflux of nervous force in them ;and when making the experiment upon himself, a painful 474 DUALISM DEMONSTRATED. tension in the joint itself, as though enduring great strain, whenthe mouth is opened to its widest extent. Finally, this action in the muscles would explain disloca-tion in the jaw from muscular action, and the special arrange-ments that obtain in the parts for obviating it, otherwiseinexplicable ; notably the existence and disposition of theexternal pterygoid muscles, one upon e
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