Part two. Hyoid bone

The hyoid bone lies free, suspended by muscle, and so is very mobile. The floor of the mouth and the tongue are attached to it above, and the larynx below, while behind are attached the epiglottis and the pharynx (see Fig. 6.37, p. 385).

The hyoid bone (Fig. 8.6) has a body, which is a curved sheet of bone convex forward and concave behind. On each side a greater horn projects back as a long slender process. At the junction of body and greater horn is the lesser horn, projecting up as a spike of bone.

Figure 8.6 Hyoid bone from above, with muscle attachments on the left side.

At rest the body lies just below the mandible at the level of C3 vertebra. This is the level of the lateral glossoepiglottic folds within the pharynx and marks the junction of oropharynx and laryngopharynx.

The thyrohyoid membrane is attached to the back of the upper border of the body and to the greater horns. Behind the concave posterior surface of the body is a bursa between bone and membrane, and here the thyroglossal duct made an upward detour behind the bone (see Fig. 1.22, p. 26) on its course down the neck. From the rounded upper border of the body a hyoepiglottic ligament passes back to the front of the epiglottis and raises the oral mucous membrane to form the median glossoepiglottic fold. A similar flange of fibrous tissue passes from the greater horn to the side of the epiglottis and raises the lateral glossoepiglottic fold. Attached to the lower border of the body is the upper attachment of the pretracheal fascia. In front of this sternohyoid and omohyoid are attached. Thyrohyoid is attached to the lower border of the greater horn. In front of these muscles the investing layer of deep cervical fascia has a linear attachment to the bone, which is thus subcutaneous and palpable. Just above this line is the linear attachment of mylohyoid to the body of the bone, and above this is the insertion of geniohyoid. A few fibres of genioglossus are attached to the upper border of the body.

The lesser horn gives attachment to the stylohyoid ligament, and the middle constrictor arises from it and from the whole length of the greater horn, thus anchoring the pharynx to the hyoid. Lateral to the constrictor hyoglossus arises from the whole length of the greater horn and the lateral part of the body, thus anchoring the tongue to the hyoid. The fibrous sling, through which the intermediate tendon of digastric glides freely, and the split tendon of stylohyoid are attached to the junction of the greater horn and body.