The one bone in your body that touches no other bone
Tucked in your neck between chin and Adam's apple sits a small horseshoe of bone held in place only by muscles and ligaments. The hyoid touches no other bone, yet it steadies the tongue for swallowing and speech, helps keep airways open in sleep, and decides whether a big cat roars or purrs.
At rest the hyoid lies between the base of the jaw and the third vertebra of the neck. Its name comes from Greek for shaped like the letter upsilon. Anatomists class it as an irregular bone with a central body and two pairs of projections, the greater and lesser horns. Muscles pull on it from the front, back and below, tying it to the floor of the mouth and tongue above, the larynx below, and the pharynx and epiglottis behind.
It forms from six separate centres of bone: two in the body and one in each horn. The greater horns begin to harden toward the end of fetal life, while the lesser horns may not ossify until a child's first or second year, and the joint between body and greater horns usually stays fibrous until middle age. That late hardening is why the bone rarely fractures in young people. The lingual artery, running down from the tongue, supplies its blood.
Its role in speech is debated. A modern-looking hyoid found in a Neanderthal at Kebara Cave in Israel led its discoverers to argue for a lowered larynx and human-like speech, but other researchers say the bone's shape does not reveal where the larynx sat. A lowered larynx is not unique to humans, and men, whose larynx sits lower, do not make a wider range of sounds than women or toddlers. One hypothesis links the mammalian hyoid to suckling milk. Studies also associate a lower-sitting hyoid with more severe obstructive sleep apnoea.
Evolution has reshaped it widely. It descends from part of the second gill arch of fish. Birds have one pair of horns, mammals two, and some amphibians and reptiles many. In woodpeckers the horns wrap around the back of the skull, helping cushion the brain while pecking. Lions, with a partly ossified hyoid, can roar but not purr; cheetahs and house cats, with a fully ossified one, purr instead.
Source: Hyoid bone
