Guidonian hand
In Medieval music, the Guidonian hand was a mnemonic device used to assist singers in learning to sight-sing. Some form of the device may have been used by Guido of Arezzo, a medieval music theorist who wrote a number of treatises, including one instructing singers in sightreading. The hand occurs in some manuscripts before Guido's time as a tool to find the semitone; it does not have the depicted form until the 12th century. Sigebertus Gemblacensis in 1105–10 did describe Guido using the joints of the hand to aid in teaching his hexachord. The Guidonian hand is closely linked with Guido's new ideas about how to learn music, including the use of hexachords, and the first known Western use of solfege.
Thyroid
In 1500 polymath Leonardo da Vinci provides the first illustration of the thyroid. In 1543 Anatomist Andreas Vesalius gave the first anatomic description and illustration of the gland. In 1656 the thyroid received its name, by the anatomist Thomas Wharton. The gland was named thyroid, meaning shield, as its shape resembled the shields commonly used in Ancient Greece. The English name "thyroid gland" is derived from the medical Latin used by Wharton – "glandula thyreoidea". "Glandula" means "gland" in Latin, and "thyreoidea" can be traced back to the Ancient Greek word θυρεοειδής, meaning "shield-like"/"shield-shaped".