Large mixed gland (predominantly serous). Size of a walnut; ~10–20 g; half the size of parotid. J-shaped — indented by posterior border of mylohyoid → large superficial part + small deep part, continuous around posterior border of mylohyoid.

Capsule

• Enclosed between two laminae of investing layer of deep cervical fascia (splits at greater cornu of hyoid)
• Superficial lamina → base of mandible; deep lamina → mylohyoid line of mandible

Parts

Superficial Part — fills anterior digastric triangle

• Anterior end: up to anterior belly of digastric
• Posterior end: at stylomandibular ligament (separates it from parotid gland); groove from facial artery’s cervical loop

Relations of superficial part:

Inferior (superficial) surface, deep→superficial: skin, superficial fascia (platysma + cervical branch of facial nerve), deep fascia, facial vein, submandibular lymph nodes

Lateral surface: submandibular fossa (inner mandible), medial pterygoid (near insertion), facial artery (loops down over gland then winds around lower border of mandible)

Medial surface:

Deep Part — small; deep to mylohyoid; on hyoglossus + styloglossus; extends anteriorly to posterior end of sublingual gland

Wharton’s Duct (Submandibular Duct)

• Thin-walled; ~5 cm long
• Course: from anterior end of deep part → forward on hyoglossus → between lingual nerve (above/lateral) and hypoglossal nerve (below/medial) → at anterior border of hyoglossus, lingual nerve crosses the duct (lateral → medial: above then below, like a sling) → between sublingual gland and genioglossus → opens on summit of sublingual papilla (sublingual caruncle), beside frenulum of tongue on floor of mouth

More viscous secretion than parotid → calculi more likely in Wharton’s duct than Stenson’s duct

Blood Supply

• Arterial: Facial artery (first grooves posterior end, then S-bend: loops over gland, winds over lower mandible border)
• Venous: Common facial vein or lingual vein

Lymphatic Drainage

• Submandibular lymph nodes → upper deep cervical nodes

Nerve Supply (via Submandibular Ganglion)

Secretomotor flowchart: Superior Salivatory Nucleus → facial nerve → nervus intermedius → chorda tympani → lingual nerve → submandibular ganglion (relay) → 5-6 branches directly to gland; anterior root re-enters lingual nerve → sublingual gland + anterior lingual glands

Submandibular ganglion — topographically related to lingual nerve (suspended by 2 roots); functionally connected to chorda tympani; lies on hyoglossus just above deep part of gland

Applied Anatomy

• Calculi — viscous secretion → stones; demonstrated by sialography
• Bimanual palpation — one finger in floor of mouth, one externally below mandible; assesses gland, duct, and lymph nodes
• Lymph nodes within gland — in carcinoma of tongue, metastatic nodes within gland substance may involve mandible; gland must be removed with nodes
• Spine of sphenoid injury — chorda tympani (medial to spine) + auriculotemporal nerve (lateral to spine): injury to spine may involve both → loss of secretion from all three salivary glands

The submandibular gland is one of the three pairs of salivary glands. It is a large mixed gland (both mucous and serous in nature) but predominantly serous. It is about the size of a walnut, weighs approximately 10–20 g, and is half the size of the parotid gland. It is J-shaped, being indented by the posterior border of the mylohyoid muscle, which divides it into a large superficial part and a small deep part that are continuous with each other around the posterior border of the mylohyoid.

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Capsule

The gland is partially enclosed between two layers of the investing layer of deep cervical fascia. At the greater cornu of the hyoid bone, the investing layer splits into two laminae:

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Parts

Superficial Part

The larger part; fills the anterior part of the digastric triangle, extending upwards up to the mylohyoid line. It presents two ends and three surfaces:

• Anterior end — up to the anterior belly of the digastric
• Posterior end — extends to the stylomandibular ligament (which separates it from the parotid gland); presents a groove produced by the ascending limb of the cervical loop of the facial artery

Relations of the Superficial Part

Inferior (Superficial) Surface — from superficial to deep:

Lateral Surface:

• Submandibular fossa on the inner aspect of the body of the mandible
• Medial pterygoid muscle (near its insertion)
• Facial artery — loops downwards and forwards between the bone and the gland, then winds around the lower border of the mandible at the anteroinferior angle to reach the face

Medial Surface — divided into three parts:

Deep Part

Small in size. Lies deep to the mylohyoid muscle, on the hyoglossus and styloglossus. Anteriorly extends to the posterior end of the sublingual gland.

Relations of the Deep Part:

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Wharton’s Duct (Submandibular Duct)

The duct is thin-walled and approximately 5 cm long.

Course:

1. Emerges from the anterior end of the deep part of the gland
2. Runs forwards on the hyoglossus, between the lingual nerve (above/lateral) and the hypoglossal nerve (below/medial)
3. At the anterior border of the hyoglossus, the lingual nerve crosses the duct — passing from lateral to medial (above it, then below it, like a sling)
4. Continues forward between the sublingual gland and the genioglossus
5. Opens on the summit of the sublingual papilla (sublingual caruncle), at the side of the frenulum of the tongue, on the floor of the mouth

Comparison with Stenson’s duct (parotid): Both ducts are approximately 5 cm long. Stenson’s duct opens opposite the upper second molar tooth (cheek); Wharton’s duct opens at the sublingual papilla beside the frenulum of the tongue (floor of mouth).

The submandibular gland’s secretion is more viscous than the parotid, making calculi (salivary stones) more likely in Wharton’s duct than in Stenson’s duct.

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Blood Supply

Arterial: Facial artery — which first grooves the posterior end of the gland, then makes an S-bend (two loops): first winding down over the submandibular gland, then up over the base of the mandible.

Venous: Drain into the common facial vein or lingual vein.

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Lymphatic Drainage

Lymph drains to the submandibular lymph nodes, which lie around and within the gland. Efferents pass to the upper deep cervical lymph nodes.

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Nerve Supply

The gland is supplied by branches from the submandibular ganglion, which convey three types of fibres:

Submandibular Ganglion

A parasympathetic peripheral ganglion — a relay station for secretomotor fibres. Topographically related to the lingual nerve (suspended from it by two roots); functionally connected to the chorda tympani branch of the facial nerve.

The fusiform ganglion lies on the hyoglossus muscle, just above the deep part of the submandibular gland.

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Secretomotor Innervation — Flowchart

Superior Salivatory Nucleus (pons)
         │
         │ (preganglionic parasympathetic fibres travel via)
         ▼
Facial Nerve (CN VII) → Nervus Intermedius
         │
         ▼
Chorda Tympani
         │
         │ (joins)
         ▼
Lingual Nerve (branch of V₃)
         │
         │ (via posterior root)
         ▼
Submandibular Ganglion (relay)
         │
    ┌────┴─────────────────┐
    ▼                       ▼
5-6 branches directly     Anterior root re-enters lingual nerve
to Submandibular Gland    → travels distally in lingual nerve
                          → reaches Sublingual Gland
                             and anterior lingual glands

Sympathetic fibres (vasomotor, from superior cervical ganglion) travel on the plexus around the facial artery → pass through the submandibular ganglion without relay → supply the submandibular and sublingual glands.

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Microscopic Anatomy

The submandibular gland is a compound tubuloacinar gland enclosed in a fibrous capsule, with connective tissue septa dividing it into lobes and lobules.

Secretory units (acini): Predominantly serous acini (producing thin, protein-rich secretion) with a smaller number of mucous acini (producing thick, mucin-rich secretion). Where the two occur together, serous cells form a crescent-shaped cap over the mucous acinus — the serous demilune.

Duct system (from acinus outwards):

Myoepithelial cells surround the acini and intercalated ducts; their contraction aids expulsion of secretion into the ducts.

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Applied Anatomy

Submandibular Calculi (Salivary Stones)

The secretion of the submandibular gland is more viscous, making it prone to calculi. Stones may form in the gland or the duct and can be demonstrated on radiograph by injecting radiopaque dye through the duct’s opening (sialography).

Bimanual Palpation

The submandibular gland can be palpated bimanually — one finger inside the mouth in the floor, one finger externally below the mandible — to assess the gland, its duct, and the surrounding lymph nodes.

Lymph Nodes Within the Gland

Submandibular lymph nodes lie both around and within the substance of the gland. In carcinoma of the tongue or of the gland itself, metastasis to these nodes may also involve the mandible. If nodes are affected by carcinoma of the tongue, the gland must be removed along with the nodes.

Injury to the Spine of Sphenoid

The chorda tympani (supplying secretomotor fibres to the submandibular and sublingual glands) lies medial to the spine of sphenoid; the auriculotemporal nerve (supplying secretomotor fibres to the parotid gland) lies lateral to the spine of sphenoid. Injury to the spine of sphenoid may involve both nerves, resulting in loss of secretion from all three salivary glands.

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