Which muscle forms the floor of the mouth?

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The floor of the mouth is formed by the mylohyoid muscles, which run from the inner surface of the mandible (the mylohyoid line) downward and medially to insert into the body of the hyoid bone. These paired muscles meet at the midline to create a muscular diaphragm that supports the tongue and separates the oral cavity from the neck. Because they lie directly beneath the tongue and form the foundational floor, they are the primary structures defining the bottom boundary of the mouth.

The other muscles mentioned are positioned differently: the geniohyoid sits above the mylohyoid, connecting the genial (genial) tubercles of the mandible to the hyoid and helping elevate the hyoid or pull it forward, but it does not form the floor. The anterior belly of the digastric lies more superficially and helps move the mandible or hyoid but isn’t the floor itself. The stylohyoid elevates the hyoid and also does not constitute the floor.