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Abstract:
Despite critical role of the tongue in human speech, previous
studies on evolution of speech have seldom discussed comparative
morphology of the tongue. In this study, microscopic and
macroscopic analyses were made on the tongue musculature of the
human and chimpanzee, and the results were presented as 3D
models. Histological examinations were performed only for the
human tongue with the result that the tongue tissue consisted of
five strata, stacked along the courses of the fibers of the
genioglossus muscle in proximal-distal directions. The human
tongue musculature can be divided into the inner and outer
regions: the former consists of the "stem" and "core", and the
latter of the "cover" and "fringe". Both gross dissections of the
human and chimpanzee tongue revealed that the inner region has a
regular repetition of a "structural unit", which consists of a
pair of thin muscle fiber laminae; one composed by the
genioglossus and vertical muscles, and another by the transverse
muscle. In the apex, the laminae lacked the fibers of the
genioglossus. The dissections revealed, therefore, that the human
and chimpanzee share the topologically same musculature of the
tongue. Based on these results, 3D tongue musculature models were
built for visual representation. Discussion will be made on
morphological difference between the human and chimpanzee
tongue.
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