The author investigated on the development of the tongue in 6 human embryos belonging to the stages of Streeter's horizon XV (2), XVI (2) and XVII (2) on the serial sections (20μthick). The reconstruction models were made. The results obtained are summerized as follows:
1) Mandibular swellings, tuberculum impar and copula were recognized in the embryos at the stage of horizon XV.
2) The flat elevated triangular area between both mandibular swellings and the hyoid arch in horizon XV is the primordium of the lingual body, on which a small eminence of tuberculum impar is to be seen.
3) On the anterior half of this swelling of the lingual body, there appears in horizon XVI a median sagittal lineal elevation, which may be a modification of the earlier tuberculum impar.
4) A furrow between the mandibular swellings and the swollen lingual body remains clearly on both sides. The mandibular swellings do not contribute to the formation of the lingual body.
5) The root of the tongue arises from the hyoid arches. The glossopharyngeal nerves reach clearly to the root of the tongue in horizon XVI.
6) The median sagittal swelling of copula was divided into the primordiums of epiglottis and plica aryepiglottica by a furrow in horizon XV.
7) The 3rd and 4th branchial arches contribute to the formation of lateral marginal zone of the primordium of epiglottis and plica aryepiglottica.
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