The Salivary Glands: A Gland the Facial Nerve Runs Straight Through
Three pairs of glands quietly make about a litre and a half of saliva a day — the fluid that lets you taste, swallow, speak and keep your teeth. You never think about them until one blocks with a stone at mealtimes, or swells with mumps, or dries up and leaves your mouth like sand. And the largest of them holds a secret that governs an entire branch of surgery: the nerve that moves your whole face runs straight through its middle, dividing it in two. That single relationship is why a benign lump in front of the ear is treated with the caution of brain surgery, why a scar there can later sweat when you eat, and why a surgeon operating on this gland spends the whole day protecting a nerve she must not cut.
A 40-year-old man notices a painless, slowly growing lump just in front of and below his right ear — soft, mobile, the size of a grape. It has been there for a year. His doctor does not shrug it off, and does not simply cut it out. She examines his face carefully first: can he raise both eyebrows, close both eyes tightly, bare his teeth symmetrically, whistle? All normal — and that examination is the whole point, because the lump sits in the parotid gland, and the nerve that controls every one of those movements runs through the substance of that gland. When the tumour is removed, the operation is not a simple excision but a superficial parotidectomy: the surgeon spends two hours tracing the trunk of the facial nerve from where it leaves the skull, following each of its branches out through the gland like defusing a bomb by its own wiring, lifting the tumour off them intact. Cut one branch and a corner of his face will hang slack for life. Everything about the surgery — its name, its caution, its risks — is dictated by one fact of anatomy: the facial nerve is inside the gland.
Three pairs, and a litre and a half a day
Saliva is not just water — it is lubricant, buffer, digestive enzyme and antiseptic all at once. There are three pairs of MAJOR salivary glands — the PAROTID, the SUBMANDIBULAR and the SUBLINGUAL — reinforced by hundreds of MINOR SALIVARY GLANDS scattered through the mucosa of the lips, cheeks, palate and tongue described in the mouth, tongue and teeth. Together they secrete roughly a litre to a litre and a half of saliva every day. What matters anatomically is that each gland is defined by three things: where it sits, where its DUCT opens into the mouth, and which nerve drives it to secrete. The secretomotor supply is always PARASYMPATHETIC, and it always reaches the gland by a curious detour, joining a branch of the trigeminal nerve for the final leg — the parasympathetic fibres "hitch-hiking" on a sensory nerve to be carried to their destination. Learn that pattern once and all three glands fall into place. One more distinction runs through everything: glands are SEROUS (thin, watery, enzyme-rich), MUCOUS (thick, ropey, lubricating) or MIXED, and each gland has its own recipe.
The parotid — and the nerve that runs through it
The largest salivary gland, and the only one an entire nerve is threaded through. The PAROTID GLAND is the largest of the three. It sits in front of and below the ear, wedged in the space between the ramus of the mandible in front and the mastoid process and sternocleidomastoid behind, wrapped in a tough, unyielding sheath — the PAROTID FASCIA (parotid capsule), derived from the investing layer of deep cervical fascia. That tight capsule explains a symptom: when the gland swells — in MUMPS (viral parotitis) or in bacterial parotitis — it cannot expand, and the pressure inside a capsule that will not stretch makes the swelling exquisitely, characteristically painful, worse on chewing when saliva is driven into a blocked gland. Threaded through the substance of the gland, in a plane, is the FACIAL NERVE (CN VII). After leaving the skull at the stylomastoid foramen it enters the posterior surface of the parotid and divides into its five terminal branches — temporal, zygomatic, buccal, marginal mandibular and cervical ('To Zanzibar By Motor Car') — which fan out through the gland and emerge at its anterior border to reach the muscles of facial expression, as traced in the facial nerve. That plane of nerves is used, surgically, to define an artificial SUPERFICIAL LOBE and DEEP LOBE, the superficial lying lateral to the nerve and the deep lying medial to it. Deep to the nerve, within the gland, lie two more travellers: the RETROMANDIBULAR VEIN (formed by the maxillary and superficial temporal veins) and, deepest of all, the EXTERNAL CAROTID ARTERY, which enters the gland and divides here into its terminal maxillary and superficial temporal branches, part of the vascular tree of the carotid and jugular.
The gland drains by a single stout duct, the PAROTID DUCT (Stensen's duct). It leaves the anterior border of the gland and runs FORWARD across the surface of the MASSETER muscle, a finger's breadth below the zygomatic arch; at the anterior border of masseter it turns sharply inward, PIERCES the BUCCINATOR muscle, and opens into the vestibule of the mouth on a small papilla OPPOSITE THE SECOND UPPER (maxillary) MOLAR. Its course over masseter is so constant that you can feel it as a cord by clenching the jaw, and its opening can be seen in your own mouth with a mirror. The oblique passage through buccinator is not incidental: it acts as a valve, so that when you blow out your cheeks or a trumpeter raises the pressure inside the mouth, the flattened duct is pinched shut and air is not forced back up into the gland.
Think of the facial nerve and the parotid gland the way you would think of a mature tree that a builder has, unwisely, allowed a large shrub to grow around. The trunk and its spreading branches came first; the soft mass of the gland grew up and enveloped them so completely that the branches now run buried inside it. When something goes wrong with the shrub — a tumour swelling within it — you cannot just tear it out, because the tree's branches are laced all through the thing you want to remove. You must instead find the trunk where it enters, and patiently follow every branch outward, teasing the diseased tissue off the living wires. That is exactly what a superficial parotidectomy is: not the removal of a lump, but the dissection and preservation of a nerve that happens to be surrounded by the lump. No other salivary gland — indeed almost no other gland in the body — makes the surgeon serve the nerve rather than the organ.
How the parotid is told to secrete — a hitch-hiking nerve
Every other function nearby belongs to VII — but the parotid alone is driven by IX. Here is the twist students never forget once they have been caught by it: the facial nerve runs THROUGH the parotid, but does NOT supply it. The SECRETOMOTOR (parasympathetic) drive to the parotid comes from the GLOSSOPHARYNGEAL NERVE (CN IX). The pathway is a classic of head-and-neck anatomy and worth tracing in full: preganglionic parasympathetic fibres leave CN IX in its tympanic branch, form the LESSER PETROSAL NERVE, and carry the fibres to the OTIC GANGLION, which hangs just below the foramen ovale. There the fibres synapse. The POSTGANGLIONIC fibres then jump aboard a passing sensory nerve — the AURICULOTEMPORAL NERVE, a branch of the mandibular division of the trigeminal (V3) — and ride it back to the gland. This is the 'hitch-hiking' arrangement in its purest form: a parasympathetic nerve (IX) reaching its target by borrowing a sensory nerve (V3) for the last stretch, exactly as VII borrows the lingual nerve to reach the glands below. The other nerves of the region — sensation of the overlying skin (great auricular nerve, C2–C3) and the sympathetic vasomotor supply travelling on the external carotid — are passengers too, but it is the crossed wiring of IX and V3 that generates the gland's most famous complication.
FREY'S SYNDROME is the parotid's revenge for its own strange wiring. When the auriculotemporal nerve is cut across during parotid surgery (or injured by trauma), its severed parasympathetic secretomotor fibres — the ones destined for the gland — regenerate blindly. Some of them wander into the wrong target and reinnervate the SWEAT GLANDS and cutaneous blood vessels of the overlying facial skin, which are normally sympathetic. The two systems happen to share the same neurotransmitter at the effector, acetylcholine, so the misdirected fibres work perfectly — on the wrong organ. The result is GUSTATORY SWEATING: weeks to months after the operation, every time the patient eats (or even thinks of food) and the salivary reflex fires, the cheek over the scar flushes and SWEATS instead of the gland salivating. It is harmless but disconcerting, it can be confirmed with a starch–iodine test, and it is the single most memorable consequence of the fact that parasympathetic and sympathetic fibres are chemically interchangeable at the end. One quirk of anatomy, one crossed wire, one sweating cheek at dinner.
- The PAROTID is the largest salivary gland, in front of and below the ear, wrapped in a tight PAROTID FASCIA — so mumps and parotitis are exquisitely painful, because the inflamed gland cannot expand.
- The FACIAL NERVE (VII) runs THROUGH the gland, dividing it into a surgical superficial and deep lobe; a superficial parotidectomy is the operation built entirely around preserving it. Deeper lie the retromandibular vein and the external carotid artery.
- The PAROTID (Stensen's) DUCT runs forward over masseter, pierces buccinator, and opens opposite the SECOND UPPER MOLAR.
- Secretomotor supply is PARASYMPATHETIC from the GLOSSOPHARYNGEAL nerve (IX): lesser petrosal nerve → OTIC GANGLION → hitch-hikes on the AURICULOTEMPORAL nerve (V3) back to the gland.
- FREY'S SYNDROME (gustatory sweating): after parotid surgery, cut auriculotemporal secretomotor fibres reinnervate facial sweat glands, so eating makes the cheek sweat instead of the gland salivating.
The submandibular gland — the gland the lingual nerve loops under
The second-largest gland, folded around a muscle, and the home of most salivary stones. The SUBMANDIBULAR GLAND lies in the SUBMANDIBULAR TRIANGLE, below the body of the mandible in the floor of the digastric triangle, one of the compartments mapped in the mouth, tongue and teeth. Its defining feature is that it is folded around the free POSTERIOR border of the MYLOHYOID muscle, so it is described as having a large SUPERFICIAL PART (below and lateral to mylohyoid, the part you can palpate under the jaw) and a smaller DEEP PART that hooks around the muscle's edge to lie on its upper surface in the floor of the mouth. It produces a MIXED serous-and-mucous saliva — more mucous than the parotid, more serous than the sublingual. From the deep part arises the SUBMANDIBULAR DUCT (Wharton's duct), which runs FORWARD and upward across the floor of the mouth to open at the SUBLINGUAL CARUNCLE, a small papilla beside the FRENULUM of the tongue. Along this course the duct has a famous relationship: the LINGUAL NERVE (V3, carrying with it the chorda tympani) crosses it — passing first LATERAL to the duct, then hooking UNDERNEATH it, and finally crossing back MEDIAL to it — so the nerve loops beneath the duct, crossing it TWICE. The surgeon removing this gland must remember that the lingual nerve is wrapped under Wharton's duct, and that dividing the duct without seeing the nerve risks numbing half the tongue.
Why does the submandibular gland form stones more than any other? Because everything about it works against gravity and against flow. Its saliva is the THICKEST and most MUCOUS of the major glands' watery secretions, richest in calcium and mucin. Its duct runs a long course UPHILL — the gland sits low in the neck and its duct climbs forward and upward to reach the floor of the mouth — so saliva must be pushed against the slope. And the duct kinks around the posterior border of mylohyoid. Thick secretion, an uphill duct and a bend: the perfect conditions for stasis and precipitation. Roughly EIGHT in TEN salivary stones (SIALOLITHIASIS) form in the submandibular duct or gland. The clinical signature follows directly from the anatomy of a blocked duct: pain and swelling of the gland at MEALTIMES, when saliva is stimulated but cannot escape past the stone, subsiding between meals — the picture of MEALTIME COLIC. The stone can sometimes be felt with a gloved finger in the floor of the mouth, or seen on a plain radiograph because most submandibular stones are radio-opaque.
The sublingual and minor glands — and their nerve
The smallest major gland sits like an almond under the tongue, and it fails in its own way. The SUBLINGUAL GLAND is the smallest of the three major glands, an almond-shaped gland lying directly under the mucosa of the FLOOR OF THE MOUTH, above the mylohyoid, on either side of the tongue where it raises a ridge called the sublingual fold. It has no single large duct: instead it drains by many (8–20) small ducts (the ducts of Rivinus) that open along the crest of that fold, and some of these join the submandibular duct. Its saliva is predominantly MUCOUS. Both the submandibular and the sublingual glands share the SAME secretomotor supply, and it is a different nerve from the parotid's: PARASYMPATHETIC fibres from the FACIAL NERVE (CN VII), leaving it as the CHORDA TYMPANI, which joins the LINGUAL NERVE and is carried forward to synapse in the SUBMANDIBULAR GANGLION — a tiny ganglion suspended from the lingual nerve in the floor of the mouth — from which postganglionic fibres pass to both glands. This is VII's own hitch-hike: it borrows the lingual nerve (V3) exactly as IX borrowed the auriculotemporal nerve for the parotid. The MINOR SALIVARY GLANDS — several hundred of them, scattered through the mucosa of the lips, cheeks, palate, and tongue — are mostly mucous and keep the mouth continuously moist.
A 35-year-old woman describes a pattern she has learned to dread: a few minutes into every meal, a firm painful swelling balloons up under her jaw on the left, tight and tender, only to melt away an hour or two after she finishes eating. Between meals she is completely well. This is textbook SUBMANDIBULAR SIALOLITHIASIS: a stone lodged in Wharton's duct, so that the meal-driven surge of saliva has nowhere to go and back-pressures the gland — MEALTIME COLIC. The examiner runs a finger along the floor of her mouth and feels the hard stone in the duct; a plain film confirms it, because the submandibular stone is radio-opaque. A small stone near the opening can be milked out or released by a tiny incision at the caruncle; a large one deep in the hilum may need the gland removed — carefully, because the lingual nerve loops beneath its duct. Contrast this with a different floor-of-mouth swelling: a young man with a painless, dome-shaped, bluish, translucent cyst under his tongue that has grown over weeks. That is a RANULA — a mucous retention (extravasation) cyst arising from a damaged sublingual gland or duct, named for its resemblance to a frog's translucent underbelly (rana, a frog). One gland blocks and hurts at mealtimes; its neighbour leaks and swells silently. The anatomy predicts both.
Secretions, blood supply and lymphatic drainage
Compare the three by what they make. The PAROTID is almost purely SEROUS — thin, watery, enzyme-rich (amylase). The SUBMANDIBULAR is MIXED, both serous and mucous, and produces the majority of resting (unstimulated) saliva. The SUBLINGUAL is predominantly MUCOUS — thick and lubricating. Blood supply follows the branches of the EXTERNAL CAROTID that pass through each region: the parotid is supplied by the external carotid and its branches directly (with the retromandibular vein draining it); the submandibular and sublingual glands are supplied by the FACIAL and LINGUAL arteries, part of the wider tree in the carotid and jugular, with venous drainage to the facial and lingual veins. Lymphatic drainage is the surgically crucial part. The PAROTID drains first to the PAROTID (preauricular and intraparotid) NODES and then on to the DEEP CERVICAL nodes — the intraparotid nodes matter because a skin cancer of the temple or scalp can metastasise to a node hidden inside the gland. The SUBMANDIBULAR and SUBLINGUAL glands drain to the SUBMANDIBULAR NODES and then to the DEEP CERVICAL chain, the levelled system set out in cervical lymph nodes. Knowing where each gland's lymph goes is knowing where its cancers spread.
- The SUBMANDIBULAR gland wraps around the free posterior border of MYLOHYOID (superficial + deep parts); its duct (Wharton's) runs forward to the SUBLINGUAL CARUNCLE beside the frenulum, and the LINGUAL NERVE loops UNDER the duct, crossing it twice.
- Submandibular saliva is mixed and THICK and its duct runs UPHILL — so it is the commonest site of SALIVARY STONES (~80%), giving pain and swelling at MEALTIMES.
- Submandibular AND sublingual secretomotor supply is PARASYMPATHETIC from the FACIAL nerve (VII) via the CHORDA TYMPANI → SUBMANDIBULAR GANGLION (suspended from the lingual nerve).
- The SUBLINGUAL gland is the smallest, under the tongue, draining by many small ducts (some into the submandibular duct); it is the site of a RANULA, a mucous retention cyst.
- SECRETIONS: parotid mostly SEROUS, submandibular MIXED, sublingual mostly MUCOUS. LYMPH: parotid → parotid + deep cervical nodes; submandibular/sublingual → submandibular + deep cervical nodes.
- The commonest salivary TUMOUR is a PLEOMORPHIC ADENOMA, usually in the parotid superficial lobe; dry mouth (xerostomia) comes from SJÖGREN'S SYNDROME and from the anticholinergic effect of many drugs.
- Thinking the facial nerve supplies the parotid because it runs through it. VII only passes through; the parotid's secretomotor supply is the GLOSSOPHARYNGEAL nerve (IX) via the lesser petrosal nerve, otic ganglion and auriculotemporal nerve. It is the submandibular and sublingual glands that VII supplies.
- Confusing the ducts. The PAROTID (Stensen's) duct opens on the cheek opposite the second UPPER molar; the SUBMANDIBULAR (Wharton's) duct opens under the tongue at the sublingual caruncle beside the frenulum. Swapping them is a classic slip.
- Assuming stones and swelling favour the parotid because it is largest. They favour the SUBMANDIBULAR gland, whose thicker mucous saliva and uphill, kinked duct cause ~80% of stones — the parotid's thin serous saliva and forward-draining duct resist stasis.
A surgeon removing a benign superficial-lobe parotid tumour spends most of the operation identifying and preserving a nerve running through the gland, yet that nerve is NOT the one that makes the gland secrete. Which nerve runs through the parotid, and which nerve provides its secretomotor supply?
- Three pairs of major salivary glands — parotid, submandibular, sublingual — plus scattered minor glands make ~1.5 L of saliva a day. Each is defined by its position, its duct's opening, and its (always parasympathetic) secretomotor nerve, which reaches it by hitch-hiking on a trigeminal branch.
- PAROTID: the largest, wrapped in tight fascia (so mumps is very painful); the FACIAL NERVE (VII) runs through it (superficial/deep lobes → superficial parotidectomy), with the retromandibular vein and external carotid deeper. Stensen's duct opens opposite the 2nd upper molar. Secretomotor = IX via the otic ganglion and auriculotemporal nerve; cut it in surgery → FREY'S SYNDROME.
- SUBMANDIBULAR: wraps around mylohyoid; Wharton's duct opens at the sublingual caruncle with the LINGUAL NERVE looping under it; mixed saliva + uphill duct = commonest site of STONES (mealtime pain). SUBLINGUAL: smallest, many small ducts, site of a RANULA. Both are supplied by VII via the chorda tympani and submandibular ganglion.
- Secretions: parotid mostly serous, submandibular mixed, sublingual mostly mucous. Lymph: parotid → parotid + deep cervical nodes; submandibular/sublingual → submandibular + deep cervical nodes. Clinical: mumps, sialolithiasis, pleomorphic adenoma, Frey's syndrome, ranula, Sjögren's and anticholinergic dry mouth, sialography.
- Drake RL, Vogl AW, Mitchell AWM. Gray's Anatomy for Students — Head and Neck: the salivary glands, parotid region and the facial nerve within the parotid.
- Moore KL, Dalley AF, Agur AMR. Clinically Oriented Anatomy — Parotid, submandibular and sublingual glands; their ducts, secretomotor supply and clinical correlations.
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- Snell RS. Clinical Anatomy by Regions — The salivary glands; parotidectomy and the facial nerve; sialolithiasis and Frey's syndrome.
- Last RJ. Last's Anatomy: Regional and Applied — The parotid region and the submandibular region.
- TeachMeAnatomy — The Salivary Glands (Parotid, Submandibular and Sublingual).
