part of the visceral skeleton of terrestrial vertebrates, including man, located under the tongue between the branches of the lower jaw.

The hyoid apparatus is a vestige of the gill arches of crossopterygians, which changed in the process of vertebrate evolution. It is most highly developed in apodals and the larvae of caudate amphibians. In these animals the lower section of the hyoid arch and three or four gill arches are clearly distinguishable. In acaudate amphibians all these elements merge into a broad cartilaginous plate bearing four pairs of appendages. In reptiles and birds, the unpaired elements of the gill apparatus form the elongate body of the hyoid apparatus, which serves as support for the tongue; the paired elements form no more than three pairs of appendages, or cornua (also known as horns).

In mammals, including man, the hyoid apparatus is usually called the hyoid bone, which consists of an unpaired body and two pairs of appendages—the major and minor horns. The hyoid bone is fastened by a series of neck muscles, which connect it with the lower jaw and skull and with the clavicles and sternum. In many animals it is also connected with the scapula. The muscles of the tongue also derive from the hyoid bone. The activity of these muscles causes movement of the hyoid bone, the floor of the oral cavity, the tongue, and larynx. The muscles play a large role in swallowing and sound production.