Development of Tongue - (Embryology video) 

Development of Tongue - (Embryology video)
The tongue develops in relation to the pharyngeal arches in the floor of the developing mouth. We have seen that each pharyngeal arch arises as a mesodermal thickening in the lateral wall of the foregut and that it grows ventrally to become continuous with the corresponding arch of the opposite side . The medial-most parts of the mandibular arches proliferate to form two lingual swellings . The lingual swellings are partially separated from each other by another swelling that appears in the midline. This median swelling is called the tuberculum impar. Immediately behind the tuberculum impar, the epithelium proliferates to form a downgrowth (thyroglossal duct) from which the thyroid gland develops. The site of this downgrowth is subsequently marked by a depression called the foramen caecum.
Another, midline swelling is seen in relation to the medial ends of the second, third and fourth arches. This swelling is called the hypobranchial eminence . The eminence soon shows a subdivision into a cranial part related to the second and third arches (called the copula) and a caudal part related to the 4th arch . The caudal part forms the epiglottis. The anterior two- third of the tongue is formed by fusion of:
(a)the tuberculum impar, and
(b)the two lingual swellings.
The anterior two-third of the tongue is thus derived from the mandibular arch . According to some, the tuberculum impar does not make a significant contribution to the tongue.
The posterior one-third of the tongue is formed from the cranial part of the hypobranchial eminence (copula). In this situation, the second arch mesoderm gets buried below the surface. The third arch mesoderm grows over it to fuse with the mesoderm of the first arch . The posterior one-third of the tongue is thus formed by third arch mesoderm.
The posterior-most part of the tongue is derived from the fourth arch.
In keeping with its embryological origin, the anterior two-third of the tongue is supplied by the lingual branch of the mandibular nerve, which is the post-trematic nerve of the first arch and by the chorda tympani which is the pre-trematic nerve of this arch. The posterior one-third of the tongue is supplied by the glossopharyngeal nerve, which is the nerve of the third arch. The most posterior part of the tongue is supplied by the superior laryngeal nerve, which is the nerve of the fourth arch.
TONSILS
The musculature of the tongue is derived from the occipital myotomes . This explains its nerve supply by the hypoglossal nerve, which is the nerve of these myotomes.
The epithelium of the tongue is at first made up of a single layer of cells. Later it becomes stratified and papillae become evident. Taste buds are formed in relation to the terminal branches of the innervating nerve fibres.
Development of the tongue starts in the 4th month of intrauterine life.