The tongue is an extremely sensitive organ that performs on a complex muscle background. The primary functions of the stomatognathic system, such as mastication, deglutition, and speech, require the active involvement of the tongue. Embryologically, the development of tongue is a very complicated process that starts around the fourth or fifth week of the gestation period, and its development has a marked influence on the oral cavity.The tongue begins to develop around the fourth week of intrauterine life. The first, second, third, and fourth pharyngeal arches contribute to the development of the various portions of the tongue.
DEVELOPMENT
The development begins with the growth of a medial swelling from the first pharyngeal arch, known as tuberculum impar. Gradually, two lateral lingual swellings start to grow in the 5th week from the same arch. As the lateral swellings increase in size, they eventually merge and overlap tuberculum impar. This merging leads to the formation of the anterior two-thirds of the tongue. Since the mucosa overlying this area of the tongue has its origin from the first pharyngeal arch; it receives its sensory innervation from the mandibular branch of the V cranial nerve (trigeminal nerve).
Meanwhile, from the mesoderm of the second, third, and fourth pharyngeal arches, another median swelling, known as hypobranchial eminence, begins to develop and form the posterior third of the tongue. The mucosa overlying this area of the tongue receives its sensory innervation from the IX cranial nerve (glossopharyngeal nerve). The posterior-most part of the tongue develops from a third median swelling, arising from the fourth pharyngeal arch. This area of the tongue receives its innervations from the superior laryngeal nerve.
The muscles of the tongue predominantly derive from the myoblasts which originate in the occipital somites. They receive their innervations from the XII cranial nerve (hypoglossal nerve) except the palatoglossus muscle. The muscles of the tongue include extrinsic and intrinsic muscles. The extrinsic muscles are four in number (genioglossus, palatoglossus, styloglossus, and hyoglossus) and originate from the structures adjacent to the tongue. They allow the tongue to move in all directions. On the other hand, the four paired intrinsic muscles which include superior longitudinal, inferior longitudinal, verticalis, and transverses muscle have their origin as well as insertion inside the tongue. They are responsible for changing the shape of the tongue.
The first sign of development of taste bud on the lingual epithelium occurs at the 8th week of gestation. Between the ninth and eleventh week of gestation, many taste bud primordia develop. They differentiate into different cell types around the eleventh through the thirteenth postovulatory week. During this period, taste pores also develop