Tongue

From as early as S14 it can be seen that the paired mandibular and hyoid processes meet in the middle line. There is a median protuberance at the lower edge of the mandibular arch, the tuberculum impar. The primordium of the anterior two-thirds of the tongue is formed from this and both lateral lingual swellings. The primordium of the thyroid gland is formed at the caudal end of the tuberculum impar. The second pharyngeal arch fuses just caudal to the anlage of the thyroid gland and forms the copula. The third and fourth pharyngeal arches do not yet reach the median plane. The hypopharyngeal eminence is formed in this area. The third arch gives rise to the posterior third of the tongue, which is thought to grow over the second arch. The entrance to the trachea is just caudal to the hypopharyngeal eminence.
The tongue (epithelium or mucous membrane) is formed from ectodermal and endodermal portions of the oral floor. The epiglottis, the submandibular and sublingual glands and the thyroid gland are formed from the endodermal portion. The anterior two-thirds of the tongue is separated from the posterior third by the sulcus terminalis. Tactile innervation of the anterior two-thirds is mediated by the lingual nerve (third branch of the trigeminal nerve) according to their origin from their particular pharyngeal arch. Taste innervation is mediated by the chorda tympani of the facial nerve for the anterior two-thirds, and by the glossopharyngeal nerve and vagus nerve for the posterior third. The musculature of the tongue arises from the occipital somites. The hypoglossal nerve follows the migrating precursors of the tongue muscle fibres.