Suprahyoid muscles
Suprahyoid muscles, from the perspective of ontogenesis, represent a rather heterogeneous group. This group includes derivatives of the first and second visceral (branchial) arches, as well as autochthonous muscles1. What unites these muscles is their location above the hyoid bone (os hyoideum) and their attachment to it in one way or another. It is important to note that the hyoid bone is integrated into the larynx and pharynx, meaning that the muscles moving this bone are involved in processes such as swallowing and speech. This has led to changes in the anatomy of the suprahyoid muscles compared to great apes2. Furthermore, for the effective function of the suprahyoid muscles, fixation or displacement of the hyoid bone is often necessary, which cannot occur without the participation of infrahyoid muscles and depends on certain neck positions3. Thus, it can be asserted that this muscle group is not functionally independent and operates fully only in close coordination with other neck muscles.
Suprahyoid muscles are:
The standard anterior and lateral approaches demonstrate all suprahyoid muscles, except the geniohyoid (m. geniohyoideus)
The geniohyoid muscle (m. geniohyoideus) can only be observed from unconventional positions, such as from above or behind. Additionally, in these projections, it becomes most evident that the suprahyoid muscles form the muscular framework of the floor of the mouth. (diaphragma oris).
Mylohyoid & Geniohyoid Muscles
In addition to their close proximity, these muscles share another distinctive feature: their 'Latin' names sound somewhat unusual. This is because, unlike most anatomical terms, the etymology of these words is rooted not in Latin but in Ancient Greek. For example, the word mylohyoideus is derived from the roots mylo (μῠ́λη) – molar tooth, and hy-oeides (υ-ειδής) – resembling the Greek letter 'υ' (a reference to the shape of the hyoid bone). Similarly, the word geniohyoideus contains the root géneion (γένειον) – chin.
Among all the suprahyoid muscles, the geniohyoid has the greatest capacity to move the hyoid bone anteriorly1, which is essential in the early phase of swallowing. Surgical resection of this muscle is reliably associated with swallowing disorders postoperatively2.
Digastric & Stylohyoid Muscles
The anatomy of both muscles is unique: as the name suggests, the digastric muscle consists of two parts – bellies – separated by a tendon (tendo intermedius m. digastrici). These parts develop from different branchial arches and, therefore, are innervated by different nerves1. Notably, the digastric muscle most often does not attach directly to the hyoid bone but interacts with it through a U-shaped fibrous loop located between the body and the greater horn of the hyoid bone2.
Despite its modest size, the stylohyoid muscle splits near its attachment to the hyoid bone, allowing the posterior belly of the digastric muscle to pass through
M. digastricus
M. stylohyoideus