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The mandible is the largest bone in the human skull, forming the lower jaw and shaping the lower third of the face. It is the only mobile bone in the skull and is the insertion point for a variety of muscles involved in facial expression and mastication. The muscles of mastication are responsible for chewing food and enhancing the eating process. The four main muscles of mastication are the temporalis, medial pterygoid, lateral pterygoid, and masseter muscles. These muscles attach to the rami of the mandible and facilitate movements such as elevation, depression, protrusion, retraction, and side-to-side grinding. In addition to these muscles, the mandible serves as an attachment point for several other muscles, including the mentalis, buccinator, platysma, and depressor labii inferioris. These muscles play a role in facial expressions and contribute to the overall functionality of the mandible.
| Characteristics | Values |
|---|---|
| Description | The mandible is the largest bone in the human skull, forming the lower jawline and shaping the contour of the inferior third of the face. It is also the strongest bone of the face and the only mobile bone of the skull. |
| Composition | The mandible is composed of a horseshoe-shaped body which lodges the teeth, and a pair of rami which project upwards to form a temporomandibular joint. |
| Borders | The body of the mandible has two borders: an alveolar border (superior) and a base (inferior). |
| Mandibular Symphysis | The mandibular symphysis is found anteriorly in the midline, where the two constituent fetal bones fuse after birth. |
| Mental Protuberance | The mandibular symphysis encloses a triangular eminence – the mental protuberance, which forms the shape of the chin. |
| Mental Foramen | Lateral to the mental protuberance is the mental foramen, an opening located below the second mandibular premolar tooth, which provides a passage for the mental nerve and vessels. |
| Oblique Line | A crest extending from the ramus to the body of the mandible, the oblique line provides the insertion point for the depressor anguli oris muscle. |
| Digastric Fossa | A paired depression on the lower margin of the mandibular body, located on each side of the midline. |
| Mental Spines | Paired bony eminences on the midline of the internal surface of the body, the mental spines provide the attaching point for the genioglossus and geniohyoid muscles. |
| Submandibular Fossa | A paired depression on each side of the mental spines which houses the submandibular gland. |
| Sublingual Fossa | A depression located superior to the mental spines which hosts the sublingual gland. |
| Ramus | The ramus is the vertical part of the mandible. The superior part of the ramus consists of two processes: the coronoid process (anterior process) and the condylar process (posterior process). |
| Mandibular Notch | The incisure between the coronoid process and the condylar process is called the mandibular notch and it is crossed by the masseteric nerve and vessels. |
| Coronoid Process | The coronoid process features the temporal crest, which serves as an attachment point for the temporalis muscle. |
| Condylar Process | The condylar process has an articular surface (the condyle), via which the mandible articulates with the articular tubercle of the temporal bone to form the temporomandibular joint. |
| Muscles | The mandible serves as the attachment point for various muscles, including the temporalis, masseter, medial pterygoid, lateral pterygoid, mentalis, buccinator, platysma, depressor labii inferioris, depressor anguli oris, genioglossus, geniohyoid, mylohyoid, and digastric muscles. |
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What You'll Learn
- External (lateral) surface muscles: mentalis, buccinator, platysma, depressor labii inferioris
- Internal (medial) surface muscles: genioglossus, geniohyoid, mylohyoid and digastric
- Mandibular rami muscles: masseter, temporalis, medial pterygoid and lateral pterygoid
- Coronoid process attachments: temporalis and masseter
- The oblique line: insertion point for the depressor anguli oris muscle
External (lateral) surface muscles: mentalis, buccinator, platysma, depressor labii inferioris
The mandible is the largest bone in the human skull, shaping the contour of the inferior third of the face and forming the lower jawline. It serves as an attachment point for various muscles, including the strong muscles of mastication.
The external (lateral) surface muscles of the mandible include the mentalis, buccinator, platysma, and depressor labii inferioris. These muscles play a crucial role in facial expressions and controlling the position, shape, and movement of the lips.
The mentalis muscle is a paired central muscle of the lower lip. It arises from the anterior midline mandible and inserts into the dermis of the chin skin. When the mentalis muscle contracts, it elevates the lower lip, as observed in the "pout" expression.
The buccinator muscle is involved in facial expressions and helps to control the shape and movement of the lips. It is one of the muscles of mastication, assisting in chewing and grinding food.
The platysma is a paired sheet of muscle located in the anterior neck. It is a direct tractor of the lower lip, inserting into and acting directly upon the lip without an intermediary. The platysma is also involved in producing facial expressions associated with sadness, doubt, and melancholy.
The depressor labii inferioris muscle arises from the lateral surface of the mandible, below the mental foramen. It inserts into the skin of the lower lip, blending with the orbicularis oris muscle. This muscle helps to depress and evert the lower lip, exposing the mandibular (lower) teeth during smiling. It is considered the most important muscle of the lower lip for this function.
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Internal (medial) surface muscles: genioglossus, geniohyoid, mylohyoid and digastric
The mandible is the largest bone in the human skull, forming the lower jawline and shaping the contour of the face. It serves as an insertion point for a range of muscles involved in facial expressions and complex jaw actions such as speaking, swallowing, chewing, and breathing.
The internal (medial) surface muscles that attach to the mandible include the genioglossus, geniohyoid, mylohyoid, and digastric muscles. The genioglossus muscle is innervated by the hypoglossal nerve, which controls the tongue's movement. It protrudes the tongue and deviates it towards the opposite side. When both left and right genioglossus muscles act together, they protrude the tongue directly forward and depress the centre of the tongue at its back. The contraction of this muscle is essential for stabilising and enlarging the upper airway, which is crucial in preventing airway obstruction during anaesthesia.
The geniohyoid muscle is a narrow, paired muscle that arises from the inferior mental spine and runs backward and slightly downward to insert into the hyoid bone. It brings the hyoid bone forward and upwards, dilating the upper airway and assisting in respiration. During the first act of swallowing, the geniohyoid muscle, along with the digastrici and mylohyoidei muscles, carries the hyoid bone and tongue upward and forward.
The mylohyoid muscle is a paired muscle of the neck that runs from the mandible to the hyoid bone, forming the floor of the oral cavity. It is named after its two attachments near the molar teeth. The two mylohyoid muscles unite in a midline raphe, and their fibres intermesh. They separate the sublingual space from the submandibular space and contribute to the floor of the mouth.
The digastric muscle has two bellies with different embryological origins and functions. The anterior belly is derived from the first brachial arch, while the posterior belly, which is involved in swallowing and chewing, arises from the second brachial arch. The anterior belly attaches at the digastric fossa of the mandible and extends postero-inferiorly towards the intermediate tendon. The digastric muscle divides the anterior triangle of the neck into four smaller triangles: the submandibular, carotid, submental, and inferior carotid triangles.
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Mandibular rami muscles: masseter, temporalis, medial pterygoid and lateral pterygoid
The mandible is the largest bone in the human skull, forming the lower jawline and shaping the contour of the inferior third of the face. It holds the lower teeth in place and serves as an attachment point for various muscles, including the muscles of mastication.
The mandibular rami muscles include the masseter, temporalis, medial pterygoid, and lateral pterygoid. The masseter muscle is the most powerful muscle of mastication, responsible for elevating and retracting the mandible. It has two parts: deep and superficial. The deep fibres of the masseter are important stabilisers of the temporomandibular joint (TMJ). The masseter originates from the maxillary process of the zygomatic bone and the zygomatic arch of the temporal bone, attaching to the ramus of the mandible.
The temporalis muscle is a fan-shaped muscle that fills the temporal fossa, exhibiting a continuous range of anteroposterior movements. It originates from the temporal fossa of the skull and attaches to the coronoid process of the mandible. The temporalis is responsible for elevating and retracting the mandible.
The medial pterygoid muscle has a quadrangular shape with two heads: deep and superficial. The superficial head originates from the maxillary tuberosity and the pyramidal process of the palatine bone, attaching to the ramus of the mandible near the angle of the mandible.
The lateral pterygoid muscle is a craniomandibular muscle that plays a crucial role in the inferior temporal region. It has two heads or bellies: superior and inferior. The superior belly may become active during mouth opening, protrusion, and contralateral deviation, while the inferior belly is involved in depressing, protruding, and deviating the mandible to the contralateral side. The lateral pterygoid inserts into the neck of the mandible, receiving its blood supply from the pterygoid branch of the maxillary artery.
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Coronoid process attachments: temporalis and masseter
The mandible is the largest bone in the human skull, forming the lower jawline and shaping the lower third of the face. It is also the insertion point for a range of muscles involved in facial expression, including the masseter and the temporalis muscle.
The temporalis muscle is usually described as a single layer originating at the temporal line, converging to a tendon, and inserting onto a narrow site of the coronoid process. However, recent studies have shown that the temporalis muscle can be divided into two or three separate segments. The distal attachment continues inferiorly beyond the coronoid process. The TM separates and attaches as two strong tendons on the lateral and medial sides of the coronoid process: a superficial tendon and a deep tendon. The superficial part of the TM is the large fan-shaped TM that is often described in anatomical atlases. It originates in the inferior temporal line and temporal fossa, descends into the superficial tendon infero-medially, and inserts at the apex, anterior, and posterior margins on the lateral and medial surfaces of the coronoid process.
The temporalis muscle was found to have multiple accessory attachments to adjacent structures, including the masseter and pterygoid muscles. The insertion of the temporalis muscle tendon that has been described in anatomical textbooks is often incomplete or inaccurate, focusing on its insertion onto the coronoid process without any description of its accessory attachments onto the adjacent structures. The point of insertion for all the temporalis muscles was the anterior border of the coronoid process; in nine cases, it was also inserted at the medial surface of the coronoid process.
The masseter muscle, meanwhile, attaches to the rami of the mandible. The ramus is the vertical part of the mandible, and the point at which it unites with the body is called the angle of mandible (or gonial angle). The superior part of the ramus consists of two processes: the coronoid process (anterior) and the condylar process (posterior). The masseteric nerve and vessels cross the incisure between these two processes, known as the mandibular notch.
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The oblique line: insertion point for the depressor anguli oris muscle
The mandible is the largest bone in the human skull, forming the lower jaw and shaping the lower third of the face. It is also the only mobile bone in the skull. The mandible serves as an attachment point for various muscles, including the muscles of mastication. The mandible is also the insertion point for a range of muscles involved in facial expressions.
The oblique line is a crest extending from the ramus to the body of the mandible. The ramus is the vertical part of the mandible, and the point at which it unites with the body is called the angle of the mandible. The oblique line begins on the external surface of the body of the mandible and extends superiorly.
The oblique line provides the insertion point for the depressor anguli oris muscle. This muscle originates from the mental tubercle and the oblique line of the mandible. The depressor anguli oris muscle fibres converge into a narrow fascicle running superiorly towards the angle of the mouth. It then blends with other muscles that insert into the lips. The depressor anguli oris muscle depresses the angle of the mouth and draws it laterally. This action is used when opening the mouth and when expressing sadness.
The depressor anguli oris muscle is part of the buccolabial group of facial muscles, which also includes the levator labii superioris alaeque nasi, levator labii superioris, zygomaticus major, zygomaticus minor, levator anguli oris, risorius, depressor labii inferioris, mentalis, orbicularis oris, incisivus superior, incisivus inferior, and buccinator muscles. The buccolabial group of muscles are involved in facial expressions.
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Frequently asked questions
The mandible is the largest and strongest bone of the face. It forms the lower jaw and holds the lower teeth in place.
The external or lateral surface of the mandible includes the mentalis, buccinator, platysma, depressor labii inferioris, and depressor anguli oris muscles.
The internal or medial surface of the mandible includes the genioglossus, geniohyoid, mylohyoid, and digastric muscles.
The mandibular rami are a pair of projections that extend perpendicularly upwards from the angle of the mandible. The masseter, temporalis, medial pterygoid, and lateral pterygoid muscles attach to the rami.
The muscles that attach to the mandible are involved in facial expression and mastication (chewing). They enable movements of the jaw such as elevation, depression, protrusion, retraction, and side-to-side motion for grinding food.
