The mylohyoid muscle or diaphragma oris is a paired muscle of the neck. It runs from the

mandible In anatomy, the mandible, lower jaw or jawbone is the largest, strongest and lowest bone in the human facial skeleton. It forms the lower jaw and holds the lower teeth in place. The mandible sits beneath the maxilla. It is the only movable bone ...

to the hyoid bone, forming the floor of the oral cavity of the mouth. It is named after its two attachments near the molar teeth. It forms the floor of the

submental triangle The submental triangle (or suprahyoid triangle) is a division of the anterior triangle of the neck. Boundaries It is limited to: * Lateral (away from the midline), formed by the anterior belly of the digastricus * Medial (towards the midline), f ...

. It elevates the hyoid bone and the

tongue The tongue is a muscular organ in the mouth of a typical tetrapod. It manipulates food for mastication and swallowing as part of the digestive process, and is the primary organ of taste. The tongue's upper surface (dorsum) is covered by taste ...

, important during swallowing and speaking.

Structure

The mylohyoid muscle is flat and triangular, and is situated immediately superior to the anterior belly of the digastric muscle. It is a pharyngeal muscle (derived from the

first pharyngeal arch The pharyngeal arches, also known as visceral arches'','' are structures seen in the embryonic development of vertebrates that are recognisable precursors for many structures. In fish, the arches are known as the branchial arches, or gill arche ...

) and classified as one of the suprahyoid muscles. Together, the paired mylohyoid muscles form a muscular floor for the oral cavity of the mouth. The two mylohyoid muscles arise from the mandible at the

mylohyoid line The mylohyoid line is a bony ridge on the internal surface of the mandible. It runs posterosuperiorly. It is the site of origin of the mylohyoid muscle, the superior pharyngeal constrictor muscle, and the pterygomandibular raphe. Structure The ...

, which extends from the mandibular symphysis in front to the last

molar tooth The molars or molar teeth are large, flat teeth at the back of the mouth. They are more developed in mammals. They are used primarily to grind food during chewing. The name ''molar'' derives from Latin, ''molaris dens'', meaning "millstone to ...

behind. The posterior fibers pass inferomedially and insert at anterior surface of the hyoid bone. The medial fibres of the two mylohyoid muscles unite in a midline

raphe Raphe (; from Greek ῥαφή, "seam"Liddell, H.G. & Scott, R. (1940). ''A Greek-English Lexicon. revised and augmented throughout by Sir Henry Stuart Jones. with the assistance of. Roderick McKenzie.'' Oxford: Clarendon Press.) has several diffe ...

(where the two muscles intermesh). The mylohyoid muscle separates the sublingual space from the submandibular space, which communicate via a lateral gap between the mylohyoid and hyoglossus muscles at the posterior free margin of mylohyoid muscle. The submandibular gland wraps around the edges of the mylohyoid, and is divided into superficial and deep lobes above and below the muscle.

Nerve supply

The mylohyoid muscle is supplied by a branch of the mandibular nerve, the inferior alveolar nerve. The

mylohyoid nerve The mylohyoid nerve (or nerve to mylohyoid) is a nerve of the head. It is a branch of the inferior alveolar nerve. It supplies the mylohyoid muscle, and the Anterior belly of digastric, anterior belly of the digastric muscle. It may also supply m ...

is a branch of the inferior alveolar nerve. The mylohyoid nerve emerges to give motor supply to the mylohyoid muscle.

Development

The mylohyoid muscles are derived from

embryonic Embryonic may refer to: *Of or relating to an embryo * ''Embryonic'' (album), a 2009 studio album by the Flaming Lips *''Embryonics ''Embryonics'' is a double-CD compilation of tracks by the Australian progressive metal band, Alchemist. It w ...

mesoderm, specifically the

Variations

The mylohyoid muscle may be united to or replaced by the anterior belly of the digastric muscle; accessory

slips Slips (or SLIPS) may refer to: *Slips (oil drilling) *SLIPS (Slippery Liquid Infused Porous Surfaces) *SLIPS (company) *SLIPS (Sri Lanka Interbank Payment System) *Slip (cricket), often used in the plural form *The Slips, a UK electronic music duo ...

to other hyoid muscles are frequent. This median raphé is sometimes absent; the fibers of the two muscles are then continuous. Variations in the mylohyoid muscle itself are not common. Accessory mylohyoid muscles have been seen in some people, which have the same attachments, nerve supply, and function. The mylohyoid muscle may also be split into an anterior portion and a posterior portion, with the sublingual gland occupying the space between these portions. An area of herniation of the sublingual gland, blood vessels, or fat, may be present, with studies reporting this in 10-50% of people.

Function

The mylohyoid muscle elevates the hyoid bone and the

. This is particularly important during swallowing and speaking. Alternatively, if other muscles are used to keep the position of the hyoid bone fixed, then the mylohyoid muscle depresses the mandible. It also functions as reinforcing the floor of mouth.

Clinical significance

The mylohyoid muscle may be imaged by CT or

MRI Magnetic resonance imaging (MRI) is a medical imaging technique used in radiology to form pictures of the anatomy and the physiological processes of the body. MRI scanners use strong magnetic fields, magnetic field gradients, and radio waves ...

. The mylohyoid separates the submandibular space below from the sublingual space above. Around the posterior border of the mylohoid muscle, these spaces communicate. Infections, especially

odontogenic infection An odontogenic infection is an infection that originates within a tooth or in the closely surrounding tissues. The term is derived from '' odonto-'' (Ancient Greek: , – 'tooth') and '' -genic'' (Ancient Greek: , ; – 'birth'). The most common ...

s can spread from one space to the other via this communication, or alternatively penetrate the mylohyoid muscle, which is a poor barrier to the spread of infection. Because the attachment of the mylohyoid muscle (the mylohoid line of the

) becomes more superior towards the posterior of the mandible, posterior infected teeth are more likely to drain into the submandibular space, and infected anterior teeth are more likely to drain into the sublingual space, since the apices of the teeth are more likely to be below and above the mylohoid line respectively (see diagram).

History

The myloyoid muscle may also be known as the diaphragma oris muscle. It is named after its two attachments near the molar teeth ("''mylo''" comes from the Greek word for "molar").http://www.anatomy.usyd.edu.au/glossary/glossary.cgi?page=m

Additional images

File:Sobo 1909 255.png, Anterior view File:Sobo 1909 265.png, Medial view File:Braus 1921 371.png, The origin of the mylohyoid muscle, inferior view. File:Braus 1921 360.png, The insertion of the mylohyoid muscle on the hyoid bone. File:Gray186.png, Hyoid bone. Anterior surface. Enlarged. File:Slide2e.JPG, Mylohyoid muscle