In the early months of fetal life, what is to be the thyroid gland is located at the base of the tongue in a depression, the foramen caecum, the upper end of the thyroglossal duct. Normally it descends along the duct to its position in front of the cricoid cartilage and the upper tracheal rings, where the duct ends.
Rarely this descent is interfered with, and the gland develops in whole or in part at the foramen caecum, forming a lingual thyroid. Still more rarely some of the cells lodge in or at the bottom of the tongue, and an intralingual or sublingual thyroid results. An accessory thyroid also sometimes occurs in front of the larynx, forming a prelaryngeal thyroid. Then comes the usual or normal position of the thyroid in front of the cricoid cartilage and the upper tracheal rings. According to Lahey,1 the lateral lobes of the thyroid
CARROLL SMITH. LINGUAL THYROID. Arch Otolaryngol. 1939;29(1):78–81. doi:10.1001/archotol.1939.00650050086008