The tongue appears in embryos of approximately 4 weeks in the form of two lateral lingual swellings and one medial swelling, the tuberculum impar

(Fig. 15.17, A and C). These three swellings originate from the first pharyngeal arch. A second median swelling, the copula, or hypobranchial eminence, is formed by mesoderm of the second, third, and part of the fourth arch. Finally, a third median swelling, formed by the posterior part of the fourth arch, marks development of the epiglottis. Immediately behind this swelling is the laryngeal orifice, which is flanked by the arytenoid swellings (Fig. 15.17,A and C ).

As the lateral lingual swellings increase in size, they overgrow the tubercu-lum impar and merge, forming the anterior two-thirds, or body, of the tongue (Fig. 15.17, B and D). Since the mucosa covering the body of the tongue originates from the first pharyngeal arch, sensory innervation to this area is by the mandibular branch of the trigeminal nerve. The body of the tongue is separated from the posterior third by a V-shaped groove, the terminal sulcus (Fig. 15.17, B and D).

The posterior part, or root, of the tongue originates from the second, third, and part of the fourth pharyngeal arch. The fact that sensory innervation to this part of the tongue is supplied by the glossopharyngeal nerve indicates that tissue of the third arch overgrows that of the second.

The epiglottis and the extreme posterior part of the tongue are innervated by the superior laryngeal nerve, reflecting their development from the fourth arch. Some of the tongue muscles probably differentiate in situ, but most are derived from myoblasts originating in occipital somites. Thus, tongue musculature is innervated by the hypoglossal nerve.

The general sensory innervation of the tongue is easy to understand. The body is supplied by the trigeminal nerve, the nerve of the first arch; that of the root is supplied by the glossopharyngeal and vagus nerves, the nerves of the third and fourth arches, respectively. Special sensory innervation (taste)

Lateral lingual swelling i

Tuberculum impar

Tuberculum impar

Terminal sulcus V

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