Overview
The hyoid apparatus (apparatus hyoideus) is a set of small bones and cartilages hanging from the base of the skull that supports the root of the tongue and suspends the larynx. Its central piece is the basihyoid, an unpaired transverse bone in the floor of the pharynx between the mandibular rami; from it the horns run craniodorsally to the skull and the thyrohyoids run caudally to the larynx.
The model comes from a plastinate in which the hyoid is preserved articulated with the larynx (epiglottic, thyroid, arytenoid and cricoid cartilages) and the start of the trachea. Only the hyoid is bone; the larynx is shown because it forms a functional unit with it.
Key features
- Basihyoid (basihyoideum): transverse body, palpable between the mandibular rami in a relaxed dog.
- Rostral horns: ceratohyoid, epihyoid and stylohyoid, chained from the basihyoid to the tympanohyoid, which is cartilaginous and attaches to the mastoid process of the temporal bone.
- Caudal horns (thyrohyoids): join the basihyoid to the lamina of the thyroid cartilage.
- Muscles: the hyoid muscles (mylohyoideus, geniohyoideus, sternohyoideus, thyrohyoideus) move the tongue and larynx during swallowing, breathing and vocalisation.
Clinical relevance
The hyoid takes part in swallowing and in positioning the larynx; its fracture or luxation (cervical trauma, bite wounds) causes dysphagia and dysphonia. It is a radiographic landmark for the larynx and for diagnosing laryngeal paralysis and laryngeal collapse in brachycephalic breeds. In laryngeal surgery (arytenoid lateralisation) and tracheostomy the basihyoid and thyroid cartilage are identified.