- the digastric
- the stylohyoid
- the mylohyoid and
- the geniohyoid.
- First layer formed by digastric and stylohyoid.
- Second layer formed by mylohyoid
- Third layer formed by geniohyoid and hyoglossus
- Fourth layer formed by genioglossus
Digastric Muscle
Origin:
- Anterior belly - from the digastric fossa of mandible
- Posterior belly - from the mastoid notch of temporal bone
Insertion: both heads meet at the intermediate tendon, which perforates Stylohyoid muscle.
Held by the the fibrous pulley to the hyoid bone
Nerve Supply:
- Anterior belly - Nerve to mylohyoid
- Posterior belly - Facial nerve
Action:
- depression of mandible, when mouth is opened widely or against resistance
- elevates the hyoid bone
RELATIONS OF POSTERIOR BELLY OF DIGASTRIC
Superficial
- Mastoid process with the sternocleidomastoid,splenius capitis and the longissimus capitis
- The stylohyoid.
- The parotid gland with retromandibular vein.
- Submandibular salivary gland and lymph nodes.
- Angle of the mandible with medial pterygoid.
Deep
- Transverse process of the atlas with superior oblique and the rectus capitis lateralis.
- Internal carotid, external carotid, lingual, facial and occipital arteries
- Internal jugular vein.
- Vagus, accessory and hypoglossal cranial nerves
- The hyoglossus muscle.
Upper Border
- The posterior auricular artery
- The stylohyoid muscle.
Lower Border
- Lower border is related to occipital artery
Stylohyoid
Origin: Posterior surface of styloid process
Insertion: Junction of the body & greater cornua of hyoid bone
Nerve supply: Facial Nerve
Action:
- Pulls the hyoid bone upwards & backwards
- with other hyoid muscles, it fixes the hyoid bone
Mylohyoid
flat, triangular muscle.
both side muscles form the floor of mouth cavity
Origin: Mylohyoid line of the mandible
Insertion:
- Posterior fibres to the body of hyoid bone
- Middle & anterior fibres form the median raphe extends between mandible & hyoid bone.
Nerve Supply: Nerve to mylohyoid
Action:
- elevates the floor of the mouth during the first stage of deglutition
- helps in depression of mandible & elevation of hyoid bone
RELATIONS OF MYLOHYOID
Superficial
- Anterior belly of the digastric
- Superficial part of the submandibular salivary gland.
- Mylohyoid nerve and vessels.
- Submental branch of the facial artery.
Deep
- Hyoglossus with its superficial relations, namely the styloglossus, the lingual nerve, the submandibular ganglion, the deep part of the submandibular salivary gland, the submandibular duct, the hypoglossal nerve, and the venae comitantes hypoglossi
- The genioglossus with its superficial relations, namely the sublingual salivary gland, the lingual nerve, submandibular duct, the lingual artery, and the hypoglossal nerve
Geniohyoid
Origin: from Inferior genial tubercles or mental spines
Insertion: into the anterior surface of body of hyoid bone
Nerve Supply: C1 through hypoglossal Nerve
Action:
- elevates the hyoid bone
- depresses the mandible with hyoid bone fixed
Hyoglossus
muscle of the tongue
Origin: from whole length of greater cornua & lateral part of the body of hyoid bone
Insertion: to the sides of the tongue in between styloglossus & inferior longitudinal muscles
Nerve supply: Hypoglossal nerve
Action:
- depresses the tongue
- makes the dorsum convex
- retracts the protruded tongue
RELATIONS OF HYOGLOSSUS
Superficial
- Styloglossus,
- lingual nerve,
- submandibular ganglion,
- deep part of the submandibular gland,
- submandibular duct,
- hypoglossal nerve and veins accompanying it.
Deep
- Inferior longitudinal muscle of the tongue.
- Genioglossus.
- Middle constrictor of the pharynx.
- Glossopharyngeal nerve.
- Stylohyoid ligament.
- Lingual artery.
Structures passing deep to posterior border of hyoglossus, from above downwards:
1. Glossopharyngeal nerve.
2. Stylohyoid ligament.
3. Lingual artery
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