The mylohyoid muscle or diaphragma oris is a paired

muscle Muscle is a soft tissue, one of the four basic types of animal tissue. There are three types of muscle tissue in vertebrates: skeletal muscle, cardiac muscle, and smooth muscle. Muscle tissue gives skeletal muscles the ability to muscle contra ...

of the neck. It runs from the

mandible In jawed vertebrates, the mandible (from the Latin ''mandibula'', 'for chewing'), lower jaw, or jawbone is a bone that makes up the lowerand typically more mobilecomponent of the mouth (the upper jaw being known as the maxilla). The jawbone i ...

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 verte ...

, forming the floor of the oral cavity of the

mouth A mouth also referred to as the oral is the body orifice through which many animals ingest food and animal communication#Auditory, vocalize. The body cavity immediately behind the mouth opening, known as the oral cavity (or in Latin), is also t ...

. It is named after its two attachments near the

molar teeth 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 toot ...

. 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 Muscle, muscular organ (anatomy), organ in the mouth of a typical tetrapod. It manipulates food for chewing and swallowing as part of the digestive system, digestive process, and is the primary organ of taste. The tongue's upper s ...

, important during

swallowing Swallowing, also called deglutition or inglutition in scientific and medical contexts, is a physical process of an animal's digestive tract (e.g. that of a human body) that allows for an ingested substance (typically food) to pass from the mou ...

and

speaking Speech is the use of the human voice as a medium for language. Spoken language combines vowel and consonant sounds to form units of meaning like words, which belong to a language's lexicon. There are many different intentional speech acts, su ...

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 transient structures seen in the embryonic development of humans and other vertebrates, that are recognisable precursors for many structures. In fish, the arches support the gills a ...

) and classified as one of the

suprahyoid muscles The suprahyoid muscles are four muscles located above the hyoid bone in the neck. They are the digastric, stylohyoid, geniohyoid, and mylohyoid muscles. They are all pharyngeal muscles, with the exception of the geniohyoid muscle. The digastr ...

. 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 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 human anatomy, the facial skeleton of the skull the external surface of the mandible is marked in the median line by a faint ridge, indicating the mandibular symphysis (Latin: ''symphysis menti'') or line of junction where the two lateral ha ...

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 toot ...

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 ;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. : raphae or raphes) has several differe ...

(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 is a thin and quadrilateral extrinsic muscle of the tongue. It originates from the hyoid bone; it inserts onto the side of the tongue. It is innervated by the hypoglossal nerve (cranial nerve XII). It acts to depress and retract th ...

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

, the

inferior alveolar nerve The inferior alveolar nerve (IAN) (also the inferior dental nerve) is a sensory branch of the mandibular nerve (CN V3) (which is itself the third branch of the trigeminal nerve (CN V)). The nerve provides sensory innervation to the lower/mandibu ...

. 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 ...

, 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 bilaterally paired suprahyoid muscle located under the jaw. Its posterior belly is attached to the mastoid notch of temporal bone, and its anterior belly ...

; accessory

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

* ...

to other hyoid muscles are frequent. This median raphe 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 sublingual gland (''glandula sublingualis'') is a seromucous polystomatic exocrine gland. Located underneath the oral diaphragm (''diaphragma oris''), the sublingual gland is the smallest and most diffuse of the three major salivary glands of ...

occupying the space between these portions. An area of

hernia A hernia (: hernias or herniae, from Latin, meaning 'rupture') is the abnormal exit of tissue or an organ (anatomy), organ, such as the bowel, through the wall of the cavity in which it normally resides. The term is also used for the normal Devel ...

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

. 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 infections 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 tissue (biology), tissues by pathogens, their multiplication, and the reaction of host (biology), host tissues to the infectious agent and the toxins they produce. An infectious disease, also known as a transmis ...

. 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 mylohyoid muscle may also be known as the diaphragma oris muscle. It is named after its two attachments near the

("''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