It lies under cover of the body of the mandible, between the mandible and the hyoid bone. The superficial part includes the submental and digastric triangles, while the deep part includes the floor of mouth and the root of the tongue.
The submandibular region contains the following structures:
Muscles: suprahyoid muscles [digastric, stylohyoid, mylohyoid, and geniohyoid] and three of the extrinsic muscles of the tongue [hyoglossus, styloglossus, and genioglossus].
Salivary glands: submandibular and sublingual glands.
Nerves: lingual nerve, hypoglossal nerve, and the glossopharyngeal nerve.
Parasympathetic ganglion: the submandibular ganglion.
Muscles of the submandibular region Digastric muscle:
It has two bellies [anterior and posterior] with intermediate tendon.
Anterior belly: it arises from the digastric fossa of the mandible [lower border of the body of mandible near the midline], and runs downwards and backwards, to end in intermediate tendon.
Posterior belly: it arises from the medial surface of mastoid process, passes downwards and forwards across the carotid sheath, and ends in intermediate tendon.
Intermediate tendon: anterior and posterior bellies are united by an intermediate tendon which pierces the stylohyoid insertion and is held in position by loop of deep fascia, which binds the tendon to the hyoid bone.
Nerve supply: anterior belly by the nerve to mylohyoid, posterior belly by the facial nerve.
Action: it depresses the mandible when the hyoid bone is fixed. Also it elevates the hyoid bone.
Insertion: it descends along the upper border of posterior belly of digastric to insert into the hyoid bone. It is pierced by the intermediate tendon of digastric muscle near its insertion.
Nerve supply: facial nerve
Action: pulls the hyoid bone upwards and backwards.
Origin: flat triangular muscle that form the floor of mouth cavity. It arises from whole length of the mylohyoid line of the mandible.
Insertion: its fibers run downward, forward and medially. The posterior fibers are inserted into the body of the hyoid bone, while the anterior fibers are inserted into the median fibrous raphe [extend from the symphysis menti to the body of the hyoid bone].
The two muscles form a muscular sheet that supports the tongue and the floor of the mouth.
When the mandible is fixed, they elevate the floor of mouth and the hyoid bone.
When the hyoid bone is fixed, they depress the mandible and open the mouth.
Origin: slender muscle that arises from the lower mental spine
Insertion: it passes backwards and downwards to insert into the body of the hyoid bone. The two muscles lie side by side between the mylohyoid muscle and the base of the tongue; on the floor of the mouth [its medial surface lies in contact with the corresponding muscle of opposite side.
Nerve supply: ventral ramus of C1 via the hypoglossal nerve.
Action: it pulls the hyoid bone forwards and upwards; also it depresses the mandible when the hyoid bone is fixed.
Origin: it is a fan shape muscle that forms the main bulk of the tongue. It arises from upper mental spine
Insertion: its fibers spread out into the tongue in vertical plane so:
The upper fibers are inserted into the tip of tongue.
The middle fibers are inserted into the dorsum of the tongue.
The lower fibers are inserted into the body of the hyoid bone.