Development of the tongue

The tongue is a muscular structure as well as a sensory organ that starts developing alongside the external face around week 4 of intrauterine life.

A fully developed tongue consists of two parts, the anterior two-thirds; and posterior one-third, which is called the root of the tongue; they are separated from each other by a shallow v-shaped groove, known as the terminal sulcus.

The two parts develop separately, which results in them having different nerve supplies.

Around week 4 of embryonic development, as a result of the folding of the embryo along the rostrocaudal axis and the lateral axis, the embryo takes on a more recognizably “human” form—but to be honest, it still looks more like a shrimp than a baby.

At the head end of this little shrimp-like creature, the neural tube expands greatly forming the primitive forebrain, which produces a bulge known as the frontal prominence.

Lateral to the neural tube is the paraxial mesoderm, which partially segments rostrally to form somitomeres and fully segments caudally to form somites, the first in the series being the occipital somites.

At this point, a small pit called the stomodeum forms between the frontal prominence and the developing cardiac bulge, and it will eventually become the oral cavity.

At the same time, six little bulges or thickenings of the mesoderm, sprout from the primitive pharynx to become the branchial, or pharyngeal, arches.

These arches are paired, symmetrical bumps that form on each side on the lateral aspect of the embryo, in a craniocaudal fashion, going from head to tail.

At the same time, neural crest cells from the midbrain and the first two rhombomeres migrate bilaterally to the region and infiltrate the mesoderm bumps where they support the development of embryonic connective tissue needed for craniofacial development, called ectomesenchyme.

The pharyngeal arches are separated externally by small clefts on the pharyngeal wall called branchial grooves, and internally by corresponding depressions called pharyngeal pouches.