STRAIN IN THE FACIAL BONES OF MACACA FASCICULARIS

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The research proposed here will contribute to a functional understanding of the morphology of the primate facial region. The primate face is dominated by the masticatory apparatus, and therefore, this research will analyze both the nature of masticatory forces and how these forces are dissipated throughout the primate face. This will be accomplished by an analysis of in vivo strain along the facial bones of Macaca fascicularis using strain gages. Rosette strain gages (three strain-gage elements with a known orientation to one another) will be bonded directly to facial bones with a cyanacrylate adhesive. The macaque will then bite a transducer (or chew various foods), and bone strain will be monitored on a chart recorder and recorder on an FM tape recorder. In some of the proposed experiments the electrical activity of the various jaw muscles (EMG) will be monitored on an oscilloscope, and also recorded on the FM tape recorder. In order to correlate precisely the animal's behavior (jaw position) with the bone strain (and EMG) data, the animal and the chart recorder (or oscilloscope) will be videotaped. A split-screen display of both animal and the chart recorder (or oscilloscope) will be produced and recorded. The magnitude and direction of the maximum and minimum principal strains will then be determined. After surface strains have been characterized along different regions of the face (e.g. the postorbital bar, anterior root of the zygoma, supraorbital and infraorbital region), patterns of internal stress will be inferred from patterns of surface strain. This will be done in order to understand the nature of external forces (muscle and reaction forces) acting on the face, and how macaque facial bones dissipate masticatory stress.