Submandibular Region

INTRODUCTION

• The submandibular region lies between the lower border of the mandible and the hyoid bone.
• It includes the submental and submandibular triangles.

Contents of Submandibular Region

1. Suprahyoid muscles.
2. Submandibular and sublingual salivary glands.
3. Lingual, hypoglossal, and glossopharyngeal nerves and submandibular ganglion.
4. Lingual and facial arteries.
5. Root of tongue and floor of mouth.

SUPRAHYOID MUSCLES

– The muscles of the submandibular region are arranged in four layers from superficial to deep:

1. First layer: Digastric and stylohyoid.
2. Second layer: Mylohyoid.
3. Third layer: Geniohyoid and hyoglossus.
4. Fourth layer: Genioglossus.

Digastric Muscle

– The digastric muscle consists of anterior and posterior bellies connected by an intermediate tendon.

Origin

• Posterior belly: It is bipennate and arises from the mastoid notch of the temporal bone.
• Anterior belly: It is unipennate and arises from the digastric fossa on the inner surface of the mandible, near the symphysis menti.

Direction of Fibres

– The anterior belly runs downwards and backwards, while the posterior belly runs downwards and forwards.

Insertion

• Both bellies meet at an intermediate tendon near the hyoid bone.
• The tendon passes through a split in the stylohyoid muscle and is held against the hyoid bone by a U-shaped fibrous sling derived from the deep cervical fascia.

Innervation

• Anterior belly: It is supplied by the nerve to mylohyoid, a branch of the inferior alveolar nerve (V3). It develops from the first pharyngeal arch.
• Posterior belly: It is supplied by the facial nerve (CN VII). It develops from the second pharyngeal arch.

Actions

• It depresses the mandible during forceful mouth opening when the hyoid bone is fixed.
• It elevates and stabilises the hyoid bone during swallowing.

Relation of the posterior belly of digastric

Superficial Relations

– The following structures lie superficial to the posterior belly of digastric:

1. Skin.
2. Superficial fascia containing platysma and cervical branch of facial nerve.
3. Investing layer of deep cervical fascia.
4. Mastoid process and sternocleidomastoid.
5. Parotid gland.
6. Retromandibular vein.
7. Submandibular gland and lymph nodes.
8. Angle of mandible.

Deep Relations

– The following structures lie deep to the muscle, from anterior to posterior:

1. Lingual artery.
2. Hypoglossal nerve.
3. Facial artery.
4. External carotid artery.
5. Internal carotid artery.
6. Hypoglossal, vagus, and accessory nerves.
7. Internal jugular vein.

Relations Along the Borders

• Upper border: It is related to the stylohyoid muscle and posterior auricular artery.
• Lower border: It is related to the occipital artery.

Stylohyoid Muscle

– The stylohyoid is a slender muscle lying along the upper border of the posterior belly of digastric.

Origin

• It arises from the posterior surface of the styloid process of the temporal bone.
• Its fibres pass downwards and forwards.

Insertion

• It attaches to the body of the hyoid bone near its junction with the greater horn.
• Its tendon splits around the intermediate tendon of the digastric muscle.

Innervation

– It is supplied by the facial nerve (CN VII), as it develops from the second pharyngeal arch.

Actions

– It elevates and retracts the hyoid bone during swallowing.

Mylohyoid Muscle

• The mylohyoid is a flat, triangular muscle forming the muscular floor of the mouth.
• The two mylohyoid muscles meet at a median fibrous raphe and together form the diaphragma oris.

Origin

• It arises from the mylohyoid line on the inner surface of the mandible.
• Its fibres pass downwards and medially.

Insertion

• Anterior fibres: They attach to the median fibrous raphe extending from the mandibular symphysis towards the hyoid bone.
• Posterior fibres: They attach to the body of the hyoid bone.

Innervation

• It is supplied by the nerve to mylohyoid, a branch of the inferior alveolar nerve (V3).
• It develops from the first pharyngeal arch.

Action

• It forms the floor of the mouth and supports the tongue.
• It elevates the floor of the mouth and tongue during the initial stage of swallowing.
• It elevates and stabilises the hyoid bone.

Geniohyoid Muscle

– The geniohyoid is a short, narrow muscle situated near the midline, superior to mylohyoid.

Origin

• It arises from the inferior genial tubercle of the mandible.
• Its fibres run backwards and downwards.

Insertion

– It attaches to the anterior surface of the body of the hyoid bone.

Innervation

– It is supplied by C1 fibres carried by the hypoglossal nerve.

Actions

• It elevates and draws the hyoid bone forwards.
• It shortens the floor of the mouth and assists in widening the pharynx during swallowing.
• It helps depress the mandible when the hyoid bone is fixed.

Practical Note: The geniohyoid becomes visible after reflecting the mylohyoid muscle.

Hyoglossus Muscle

• The hyoglossus is a flat, quadrilateral extrinsic muscle of the tongue.
• It is considered the key muscle of the submandibular region because of its important neurovascular relations.

Origin

• It arises from the superior surface of the greater horn and adjoining lateral part of the body of the hyoid bone.
• Its fibres ascend almost vertically towards the tongue, deep to mylohyoid.

Insertion

– It inserts into the lateral part of the tongue between styloglossus laterally and the inferior longitudinal muscle medially.

Innervation

– It is supplied by the hypoglossal nerve (CN XII), as it develops from occipital myotomes.

Actions

• It depresses the sides of the tongue, making its dorsal surface more convex.
• It assists in retracting the protruded tongue.

Styloglossus Muscle

– The styloglossus is a slender extrinsic muscle extending from the styloid process to the tongue.

Origin

• It arises from the styloid process and adjoining stylohyoid ligament.
• Its fibres pass downwards and forwards.

Insertion

– It enters the lateral part of the tongue, where its fibres blend with those of hyoglossus.

Innervation

– It is supplied by the hypoglossal nerve (CN XII).

Actions

• It retracts and elevates the tongue.
• Bilateral contraction draws the tongue backwards and upwards, forming a trough along its dorsal surface to assist swallowing.

Genioglossus

• The genioglossus is a large, fan-shaped extrinsic muscle forming a substantial part of the tongue.
• It lies deep to mylohyoid and geniohyoid and occupies the space medial to hyoglossus.

Origin

– It arises from the superior genial tubercle of the mandible.

Insertion

– Its fibres spread backwards in a fan-shaped arrangement:

• Upper fibres: They ascend and extend towards the tip of the tongue.
• Middle fibres: They pass backwards into the substance of the tongue.
• Lower fibres: They descend towards the body of the hyoid bone.

Innervation

– It is supplied by the hypoglossal nerve (CN XII) and develops from occipital myotomes.

Actions

• Unilateral contraction: It protrudes the tongue towards the opposite side.
• Bilateral contraction: It protrudes the tongue forwards in the midline.
• It also depresses the central part of the tongue.

Relations of hyoglossus

Superficial Relations

• The hyoglossus is partly covered by the mylohyoid muscle.
• The following structures lie superficial to it, from above downwards:
  • Lingual nerve.
  • Submandibular ganglion.
  • Deep part of submandibular gland.
  • Submandibular duct.
  • Hypoglossal nerve and accompanying veins.

Deep Relations

– The following structures lie deep to the hyoglossus:

1. Genioglossus.
2. Middle constrictor of pharynx.
3. Glossopharyngeal nerve.
4. Stylohyoid ligament.
5. Lingual artery.
6. Inferior longitudinal muscle of tongue.

Structures Passing Deep to the Posterior Border

– The following structures pass deep to the posterior border of hyoglossus, from above downwards:

1. Glossopharyngeal nerve.
2. Stylohyoid ligament.
3. Lingual artery.

SUBMANDIBULAR SALIVARY GLAND

• The submandibular gland is one of the three paired major salivary glands. It is a mixed seromucous gland, predominantly serous.

Dimensions

• It is roughly J-shaped, about the size of a walnut, and weighs approximately 15–20 g.

Location

• It occupies the submandibular fossa of the mandible within the digastric triangle.

Parts

• The posterior border of mylohyoid divides the gland into two continuous parts:
  • Superficial part: It is larger and lies superficial to mylohyoid.
  • Deep part: It is smaller and lies deep to mylohyoid.
• Both parts are continuous around the posterior free border of mylohyoid.

Superficial Part

Features of Superficial Part

• It is a lobulated, cream-coloured structure situated below the inferior border of the mandible.
• Extent: It extends superiorly towards the mylohyoid line and inferiorly overlaps stylohyoid and the posterior belly of digastric.
• It presents three surfaces: Inferior, lateral, and medial.

Coverings of Superficial Part

• The superficial part is partially enclosed by two layers of the investing deep cervical fascia.
• Superficial layer: It covers the inferior surface and attaches to the lower border of the mandible.
• Deep layer: It covers the medial surface and attaches to the mylohyoid line.

Relations of Superficial Part

1. Inferior (superficial) surface

– It is covered by the following structures:

1. Skin.
2. Superficial fascia containing platysma and cervical branch of facial nerve.
3. Investing layer of deep cervical fascia.
4. Facial vein.
5. Submandibular lymph nodes.

2. Lateral surface

– It is related to the following structures:

1. Submandibular fossa of mandible.
2. Medial pterygoid muscle.
3. Facial artery.

3. Medial surface

– Its relations are divided into three parts:

Anterior part

• Mylohyoid muscle.
• Nerve and vessels to mylohyoid.
• Submental branch of facial artery.

Middle part

• Hyoglossus and styloglossus muscles.
• Lingual artery.
• Hypoglossal nerve.
• Submandibular ganglion.

Posterior part

• Styloglossus and stylopharyngeus muscles.
• Stylohyoid ligament.
• Glossopharyngeal nerve.
• Pharyngeal wall.

Deep Part

Features of Deep Part

• The deep part is smaller and lies between mylohyoid laterally and hyoglossus medially.
• It continues posteriorly with the superficial part around the free border of mylohyoid.

Relations of Deep Part

• Laterally: It is related to mylohyoid.
• Medially: It is related to hyoglossus.
• Superiorly: It is related to the lingual nerve and submandibular ganglion.
• Inferiorly: It is related to the hypoglossal nerve.

Practical Note: Reflection of mylohyoid exposes the deep part of the gland and submandibular duct.

Relation of Facial Artery

• The facial artery grooves the deep aspect of the superficial part of the gland.
• It curves around the inferior border of the mandible near the anterior border of masseter.
• It then pierces the superficial layer of investing fascia to enter the face.

Submandibular Duct

– The submandibular duct, also called Wharton’s duct, is a thin-walled tube approximately 5 cm long.

Course

• It arises from the anterior end of the deep part of the submandibular gland.
• It runs forwards and upwards over hyoglossus, between the lingual nerve superiorly and hypoglossal nerve inferiorly.
• The lingual nerve loops beneath the duct near the anterior border of hyoglossus.
• The duct continues forwards between genioglossus medially and sublingual gland laterally.
• It opens on the sublingual papilla, beside the frenulum of the tongue.

Blood Supply, Lymphatic Drainage, Innervation

Blood supply

• Arterial supply: It receives branches from the facial and lingual arteries.
• Venous drainage: Blood drains through the facial and lingual venous systems.

Lymphatic drainage

– Lymph drains into the submandibular lymph nodes and subsequently into the deep cervical lymph nodes, including the jugulodigastric group.

Nerve Supply

• Parasympathetic (secretomotor): Postganglionic fibres from the submandibular ganglion stimulate salivary secretion.
• Sympathetic (vasomotor): Fibres reach the gland through the periarterial plexus surrounding the facial artery.
• Sensory: Fibres are carried by the lingual nerve, a branch of the mandibular division of the trigeminal nerve.

Submandibular ganglion

• The submandibular ganglion, also called Langley’s ganglion, is a small peripheral parasympathetic ganglion, approximately the size of a pinhead.
• Topographical connection: It is connected to the lingual nerve, a branch of the mandibular division of the trigeminal nerve (V3).
• Functional connection: It is functionally associated with the facial nerve (CN VII).

Location

• It lies on the lateral surface of the hyoglossus muscle, deep to mylohyoid.
• It is suspended from the lingual nerve by two connecting branches.

Relations

• Superiorly: Lingual nerve.
• Inferiorly: Deep part of submandibular gland.
• Superficially: Mylohyoid muscle.
• Deeply: Hyoglossus muscle.

H3: Roots and Connections

The ganglion receives three types of nerve fibres.

1. Parasympathetic (Secretomotor) Root

• Preganglionic fibres: They arise from the superior salivatory nucleus in the pons and travel through the facial nerve.
• They enter the chorda tympani, which passes through the middle ear and joins the lingual nerve in the infratemporal fossa.
• These fibres reach the submandibular ganglion through the lingual nerve and synapse within the ganglion.
• Postganglionic fibres: They supply the submandibular gland directly, while others rejoin the lingual nerve to reach the sublingual gland.

2. Sympathetic Root

• Preganglionic fibres arise mainly from the lateral horn of the T1 spinal cord segment.
• They ascend through the sympathetic trunk and synapse in the superior cervical sympathetic ganglion.
• Postganglionic fibres reach the submandibular ganglion through the periarterial plexus around the facial artery.
• They pass through the ganglion without synapsing and supply the submandibular and sublingual glands.

3. Sensory Root

• Sensory fibres from the lingual nerve pass through the ganglion without synapsing.
• They convey general sensation from the associated salivary glands.

Functions

• Parasympathetic fibres: They stimulate salivary secretion from the submandibular and sublingual glands.
• Sympathetic fibres: They regulate glandular blood flow and influence salivary secretion.
• Sensory fibres: They carry general sensory impulses from the glands.

SUBLINGUAL SALIVARY GLAND

• The sublingual gland is the smallest of the three major salivary glands.
• Shape: It is almond-shaped.
• Weight: It weighs approximately 3–4 g.
• Location: It lies in the floor of the mouth, between the oral mucosa and mylohyoid muscle.

Relations

• Anteriorly: It is related to the mandibular symphysis.
• Posteriorly: It is related to the deep part of submandibular gland.
• Superiorly: It is covered by the oral mucosa.
• Inferiorly: It rests on mylohyoid.
• Medially: It is related to genioglossus.
• Laterally: It occupies the sublingual fossa of mandible.

Ducts

• The gland has approximately 8–20 small ducts of Rivinus, most of which open along the sublingual fold in the floor of the mouth.
• Some ducts from the anterior part may unite to form the major sublingual duct (Bartholin’s duct), which joins the submandibular duct or opens separately near the sublingual papilla.

Blood Supply

– It receives arterial branches from the sublingual branch of lingual artery and submental branch of facial artery.

Lymphatic Drainage

– Lymph drains mainly into the submandibular and submental lymph nodes.

Nerve Supply

• Parasympathetic fibres: They arise from the facial nerve and reach the gland through chorda tympani, lingual nerve, and submandibular ganglion.
• Sympathetic fibres: They reach the gland through periarterial plexuses.
• Sensory fibres: They are carried by the lingual nerve.

Histology of Submandibular and Sublingual Glands

Histology of submandibular gland

• The submandibular gland is a mixed seromucous gland with predominantly serous secretory units.
• Capsule: A well-defined connective tissue capsule sends septa into the gland, dividing it into lobes and lobules.
• Secretory units: Serous and mucous acini are present. Some mucous units show serous demilunes in routinely prepared sections.
• Ducts: The duct system includes intercalated, striated, interlobular, and larger excretory ducts.
• Intercalated ducts are shorter and less prominent than those of the parotid gland.

Histology of sublingual gland

• The sublingual gland is a predominantly mucous, mixed salivary gland.
• Capsule: It has an incomplete or poorly defined connective tissue capsule.
• Secretory units: Mucous tubules predominate, with scattered serous cells and serous demilunes.
• Ducts: Intercalated ducts are poorly developed or absent, while striated ducts are short and relatively few.
• Larger interlobular and excretory ducts are present.

Development Of Submandibular And Sublingual Glands

• Both glands develop from epithelial outgrowths, traditionally described as endodermal in origin, arising from the floor of the primitive oral cavity.
• Submandibular gland: It develops from a single epithelial bud that undergoes repeated branching and canalisation to form the glandular tissue and submandibular duct.
• Sublingual gland: It develops from multiple epithelial buds in the floor of the mouth. These form separate secretory units and numerous small ducts.