The mylohyoid muscle or diaphragma oris is a paired

muscle Skeletal muscles (commonly referred to as muscles) are Organ (biology), organs of the vertebrate muscular system and typically are attached by tendons to bones of a skeleton. The muscle cells of skeletal muscles are much longer than in the other ...

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 bon ...

to the

hyoid bone The hyoid bone (lingual bone or tongue-bone) () is a horseshoe-shaped bone situated in the anterior midline of the neck between the chin and the thyroid cartilage. At rest, it lies between the base of the mandible and the third cervical verteb ...

, forming the floor of the oral cavity of the

mouth In animal anatomy, the mouth, also known as the oral cavity, or in Latin cavum oris, is the opening through which many animals take in food and issue vocal sounds. It is also the cavity lying at the upper end of the alimentary canal, bounded on t ...

. 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), ...

. It elevates the

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 bu ...

, important during

swallowing Swallowing, sometimes called deglutition in scientific contexts, is the process in the human or animal body that allows for a substance to pass from the mouth, to the pharynx, and into the esophagus, while shutting the epiglottis. Swallowing ...

and

speaking Speech is a human vocal communication using language. Each language uses phonetic combinations of vowel and consonant sounds that form the sound of its words (that is, all English words sound different from all French words, even if they are th ...

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 arch ...

) and classified as one of the suprahyoid muscles. Together, the paired mylohyoid muscles form a muscular floor for the oral cavity of the

. The two mylohyoid muscles arise from the mandible at the mylohyoid line, which extends from the

mandibular symphysis In human anatomy, the facial skeleton of the skull The skull is a bone protective cavity for the brain. The skull is composed of four types of bone i.e., cranial bones, facial bones, ear ossicles and hyoid bone. However two parts are more p ...

in front to the last molar tooth behind. The posterior fibers pass inferomedially and insert at anterior surface of the

. 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 The hyoglossus, thin and quadrilateral, arises from the side of the body and from the whole length of the greater cornu of the hyoid bone, and passes almost vertically upward to enter the side of the tongue, between the styloglossus and the in ...

muscles at the posterior free margin of mylohyoid muscle. The

submandibular gland The paired submandibular glands (historically known as submaxillary glands) are major salivary glands located beneath the floor of the mouth. They each weigh about 15 grams and contribute some 60–67% of unstimulated saliva secretion; on stimula ...

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 In neuroanatomy, the mandibular nerve (V) is the largest of the three divisions of the trigeminal nerve, the fifth cranial nerve (CN V). Unlike the other divisions of the trigeminal nerve ( ophthalmic nerve, maxillary nerve) which contain only ...

, the

inferior alveolar nerve The inferior alveolar nerve (IAN) (also the inferior dental nerve) is a branch of the mandibular nerve, which is itself the third branch of the trigeminal nerve. The inferior alveolar nerves supply sensation to the lower teeth. Structure The inf ...

. The mylohyoid nerve 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

mesoderm The mesoderm is the middle layer of the three germ layers that develops during gastrulation in the very early development of the embryo of most animals. The outer layer is the ectoderm, and the inner layer is the endoderm.Langman's Medical Emb ...

, specifically the

Variations

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

digastric muscle The digastric muscle (also digastricus) (named ''digastric'' as it has two 'bellies') is a small muscle located under the jaw. The term "digastric muscle" refers to this specific muscle. However, other muscles that have two separate muscle belli ...

; 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 The paired sublingual glands are major salivary glands in the mouth. They are the smallest, most diffuse, and the only unencapsulated major salivary glands. They provide only 3-5% of the total salivary volume. There are also two other types of sa ...

occupying the space between these portions. An area of

hernia A hernia is the abnormal exit of tissue or an organ, such as the bowel, through the wall of the cavity in which it normally resides. Various types of hernias can occur, most commonly involving the abdomen, and specifically the groin. Groin hern ...

tion of the

, blood vessels, or fat, may be present, with studies reporting this in 10-50% of people.

Function

The mylohyoid muscle elevates the

and the

. This is particularly important during

and

. 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. 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 Ancient Greek includes the forms of the Greek language used in ancient ...

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 An infection is the invasion of tissues by pathogens, their multiplication, and the reaction of host tissues to the infectious agent and the toxins they produce. An infectious disease, also known as a transmissible disease or communicable d ...

. 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