What is Dr. Zubair Khalid's research focus?

Dr. Zubair Khalid specializes in molecular virology, mRNA vaccine development, and computational biology, with a focus on avian pathogens like IBDV and Avian Reovirus.

Where is Dr. Zubair Khalid currently working?

Dr. Zubair Khalid is a Postdoctoral Research Associate at the University of Maryland (UMD), specifically within the Department of Animal and Avian Sciences.

Submandibular Gland: Anatomy, Ducts, and Comparative Notes

Name: Submandibular Gland: Anatomy, Ducts, and Comparative Notes
Creator: Dr. Zubair Khalid

By Dr. Zubair Khalid, DVM, MS, PhD · 2026-09-20

The submandibular gland is a paired, mixed seromucous salivary gland positioned in the submandibular triangle of the ventral neck, whose secretion reaches the oral cavity through the submandibular duct (Wharton's duct) and opens at the sublingual caruncle beside the frenulum of the tongue. It contributes a continuous, low-volume basal saliva that keeps the mouth moist between meals, and its size, position, and duct course differ enough across domestic species that a single mental template will mislead you in the clinic.

Understanding this gland matters for three practical reasons. First, it is the dominant or a major salivary contributor in several species, so disease here changes oral health and swallowing. Second, the duct runs a long, superficial course through the floor of the mouth, which makes it vulnerable to obstruction, calculi, and surgical injury. Third, the gland sits in a crowded anatomic neighborhood with the mandibular lymph node, the digastric and mylohyoid muscles, and the marginal mandibular branch of the facial nerve, so swelling in this region is a genuine diagnostic puzzle rather than a simple gland problem.

Orientation: Where the Submandibular Gland Sits

The submandibular triangle

The submandibular (or digastric) triangle is the anatomic home of the gland. Its borders are the ventral border of the mandible dorsally, the digastric muscle caudally, and the mylohyoid muscle medially. In species with a well-developed digastric, the gland nestles into the angle between the mandible and the digastric, partially wrapping around the muscle's rostral belly. The mylohyoid forms the floor of the mouth and separates the gland from the oral cavity proper, so the gland lies outside the mouth, ventral and lateral to the mylohyoid, while its duct crosses the mylohyoid to reach the oral floor.

This relationship is the single most useful fact for surgery. If you can identify the mylohyoid, you know which side of the floor you are on. The gland and its capsule are superficial to the mylohyoid. The duct dives deep to it.

Relations to the digastric and mylohyoid muscles

The digastric muscle has two bellies in the dog and cat, and the gland typically caps the angle of the jaw where the two bellies meet or where the muscle curves around the gland. The mylohyoid is a flat sheet. The submandibular duct passes between the mylohyoid and the hyoglossus (or the genioglossus, depending on species) as it travels rostrally. That intramuscular corridor is why the duct is described as having a submucosal segment near its opening, where it is covered only by oral mucosa and is easy to palpate or incise.

The gland is enclosed in a thin fibrous capsule that sends septa inward, dividing the parenchyma into lobules. This lobular architecture is consistent across species and is visible on imaging as a lobulated soft-tissue mass. A study of porcine submandibular glands confirmed a lobular organization akin to human glands, with mucous acinar cells, intercalated and excretory ducts, and rich vascularization [1]. The lobular pattern is what allows partial resection without destroying the whole gland, and it is also why gland tumors can grow to enormous size while remaining within a capsule.

The submandibular fossa

On the lingual surface of the mandible, from the mental foramen back to the molar region, there is a depression called the submandibular fossa that accommodates the gland. A cone-beam computed tomography study of 160 patients aged 18 to 35 years classified fossa depth into three types: Type I under 2 mm, Type II 2 to 3 mm, and Type III over 3 mm. Type I was the most common, and males had greater mean fossa depth than females [2]. This matters in veterinary dentistry and oral surgery because a deep fossa means the gland sits close to the mandibular canal, raising the risk of hemorrhage or nerve injury during implant placement or extraction in that region.

Acinar Type and Secretion

The submandibular gland is mixed, meaning it contains both serous and mucous acini. In the dog and cat, serous acini predominate, but mucous acini are present and increase in number toward the duct system. In ruminants and pigs, mucous acini are more prominent. A comparative histochemical study of ovine and caprine glands found that the mandibular gland in both sheep and goats is a mixed gland, with mucous acini that are Periodic Acid-Schiff positive and Aldehyde Fuchsin negative, and serous acini that are Aldehyde Fuchsin positive [3]. The same study found the mandibular gland of sheep was significantly larger than that of goats, while the parotid gland of goats was larger than that of sheep, a reminder that gland prominence is species-specific and not a reliable indicator of function.

The functional consequence of mixed secretion is that submandibular saliva is thicker and more mucinous than parotid saliva but less viscous than pure mucous glands like the palatine glands. This intermediate consistency supports the gland's main role: resting or basal salivation. Between meals, when the mouth is not being stimulated by chewing, the submandibular gland provides a continuous low-volume flow that lubricates the mucosa, clears debris, and maintains a film of saliva over the teeth and tongue. The parotid gland, by contrast, is largely a reflex gland that surges with eating. In species where the mandibular gland is the dominant salivary gland, loss of its secretion produces noticeable dry mouth and oral discomfort.

The Duct: Wharton's Duct and the Sublingual Caruncle

Course of the duct

Wharton's duct begins at the hilus of the gland, where the intraglandular duct system converges. A microanatomic study using methacrylate resin casts of human submandibular glands described a treelike structure in which arteries, veins, and ducts run in parallel and divide into three levels: main branches, narrower secondary branches, and further subdivisions [4]. This parallel arrangement of vessels and ducts is surgically important because it means the duct can be traced alongside its companion vessels, and it explains why duct injury often accompanies vascular injury.

From the hilus, the duct passes rostrally and medially, running along the medial surface of the gland and then deep to the digastric tendon. It crosses the mylohyoid muscle and continues forward in the floor of the mouth, where it lies just beneath the mucosa. Near its termination, the duct runs beside the sublingual gland and its smaller ducts. The submandibular duct opens at the sublingual caruncle (also called the sublingual papilla), a small mucosal elevation on the floor of the mouth beside the frenulum of the tongue. The sublingual gland's major duct often opens on or near the same caruncle, which is why the two glands are sometimes described as sharing a drainage point.

The opening and its variations

The sublingual caruncle is the landmark you look for when examining the floor of the mouth. In the dog and cat it is a small, pale, raised papilla just lateral to the frenulum. In the horse and ruminant it is larger and more prominent because the duct is longer and the gland is bigger.

Congenital anomalies of the duct opening are rare but reported. A case report described bilateral congenital duct orifice ectopia of the submandibular gland with a left sublingual gland cyst, a developmental anomaly in which the duct opening is displaced from its normal position [5]. The clinical lesson is that a missing or displaced caruncle in a young animal with oral swelling should raise suspicion of a developmental duct anomaly rather than an acquired obstruction.

How the duct is examined and tested

In practice, the duct is assessed by visual inspection of the floor of the mouth, by palpation along its course, and by imaging. Sialography, in which contrast is injected into the duct, outlines the duct lumen and reveals strictures, dilatations, or calculi. Magnetic resonance sialography (sialo-MRI) is used in human medicine to detect duct dilatation, and a study of idiopathic submandibular duct dilatation used a threshold of 4 mm or greater on sialo-MRI to define a megaduct [6]. Sialendoscopy, the endoscopic examination of the duct lumen, allows direct visualization and retrieval of stones or foreign bodies.

For the veterinary clinician, the most accessible test is gentle massage of the gland while watching the caruncle. A normal gland produces a small bead of saliva at the opening. Absent flow, purulent discharge, or a visible swelling along the duct suggests obstruction or infection.

Comparative Anatomy Across Species

The submandibular gland is present in all domestic mammals, but its relative size, position, and duct course vary. The table below summarizes the key differences.

Feature	Dog	Cat	Horse	Ruminant (cattle, sheep, goat)
Relative size	Mandibular gland is the dominant salivary gland	Moderate, closely related to mandibular lymph node	Large, elongated, extends along the jaw	Large in sheep, smaller in goats relative to parotid
Position	Submandibular triangle, wraps around digastric	Submandibular triangle, adjacent to mandibular lymph node	Caudal to the mandible, extends toward the throat	Ventral to the mandible, often covered by the parotid
Duct course	Long, crosses mylohyoid, opens at sublingual caruncle	Similar to dog, opens at sublingual caruncle	Long duct running rostral along the floor of the mouth	Duct runs rostral, opens at sublingual caruncle
Acinar type	Mixed, predominantly serous	Mixed, predominantly serous	Mixed	Mixed, more mucous in ruminants
Clinical note	Dominant gland, sialocele common	Mandibular lymph node proximity complicates swelling	Large gland, duct accessible for examination	Sheep mandibular gland larger than goat; parotid larger in goat

Dog

In the dog, the mandibular gland is the largest and most important salivary gland. It lies in the submandibular triangle, partially wrapping around the digastric muscle, and its duct runs a long course to the sublingual caruncle. Because it is the dominant gland, it produces most of the resting saliva, and its obstruction or removal causes noticeable oral dryness. Sialocele, an accumulation of saliva in the soft tissues after duct leakage, is a common clinical problem in dogs and most often involves the mandibular or sublingual gland complex.

Cat

In the cat, the submandibular gland is closely associated with the mandibular lymph node, which sits just rostral and ventral to the gland. This proximity means that swelling in the submandibular region is often lymph node enlargement rather than gland enlargement. A cat with a submandibular mass may have reactive lymphadenopathy from dental disease, lymphoma, or a salivary gland tumor, and the two cannot be distinguished by palpation alone. Fine-needle aspiration or biopsy is needed. The duct course and opening are similar to the dog.

Horse

In the horse, the submandibular gland is large and elongated, extending caudally along the jaw toward the throat. The duct is long and runs rostrally along the floor of the mouth to open at the sublingual caruncle. Because the horse is a grazing animal with a high rate of salivary flow during eating, the gland's contribution to digestion and bolus formation is significant. The large size of the gland and its duct makes it accessible to palpation per os, and duct obstruction in horses presents as a swelling in the submandibular region that may be mistaken for lymph node enlargement.

Ruminants

In ruminants, the submandibular gland is mixed and more mucous than in carnivores, consistent with the need for copious lubrication during rumination. A comparative study of sheep and goat glands found that the mandibular gland of sheep was significantly larger than that of goats, while the parotid gland of goats was significantly larger than that of sheep [3]. The same study found that the total length of the duct system was not significantly different between the two species, but the total volume of parotid ducts was significantly higher than that of mandibular ducts. This suggests that in ruminants, the parotid gland is the major ductal contributor, while the mandibular gland contributes more to the mucous component of saliva.

Clinical Relevance, Limitations and Common Mistakes

Sialolithiasis and duct obstruction

Sialolithiasis, the formation of stones in the salivary duct, occurs most often in the submandibular gland. The reason is anatomic and secretory: the submandibular duct is long, runs uphill against gravity, and carries a mixed secretion that is more viscous than parotid saliva, all of which favor stasis and mineral precipitation. A case report of a 66-year-old edentulous patient described a calculus at the duct orifice of the right submandibular gland, discovered as a foreign body on the floor of the mouth that had been present for one week without discomfort [7]. The stone was removed transorally, and the gland's texture and secretory function were normal after eight weeks of follow-up. The same report noted that sialolithiasis may remain asymptomatic throughout its course, and that early intervention can prevent severe complications [7].

A separate case described multiple submandibular duct stones in an 18-year-old patient who also had a submandibular neurilemmoma, a benign nerve sheath tumor [8]. The authors noted that most sialolithiasis occurs in the submandibular glands and is highly related to the anatomy and secretory function of the gland [8]. This case is a reminder that obstruction can have more than one cause and that a mass effect from an adjacent tumor can predispose to stone formation.

Other causes of obstruction

Not every obstruction is a stone. A case report described an ectopic deciduous canine tooth lodged inside the submandibular duct, discovered accidentally and removed by a combined intraoral sialendoscopic approach [9]. The authors noted that obstructive sialadenitis is the most prevalent salivary gland disorder, with sialolithiasis the leading cause, but that other obstructive bodies can mimic sialoliths in clinical and radiographic presentation [9]. Another report described a grass foreign body that migrated retrograde through Wharton's duct and lodged in the deep lobe of the gland, requiring sialadenectomy [10]. These cases illustrate that any radio-opaque or soft-tissue density along the duct course deserves investigation.

Duct dilatation without obstruction

Idiopathic dilatation of the submandibular duct, also called a megaduct, is a distinct entity from dilatation caused by obstruction. A retrospective study of five patients with idiopathic duct dilatation in nine submandibular glands found that the most commonly reported symptoms were submandibular swelling, pruritus, and discomfort, mostly outside mealtimes, and that recurrence of symptoms after treatment was frequent [6]. The authors noted that lithiasis and stenosis cause dilatation through increased pressure upstream of the obstruction, but idiopathic megaducts occur without associated pressure increase [6]. This distinction matters because a dilated duct on imaging does not automatically mean there is a stone to remove.

Tumors and surgical considerations

The submandibular gland can develop neoplasms, including salivary duct carcinoma and carcinoma ex-pleomorphic adenoma. A case report described a 22 cm carcinoma ex-pleomorphic adenoma arising from the submandibular gland in a 56-year-old man with a 15-year history of a slowly growing neck mass [11]. Another described salivary duct carcinoma in a patient with neurofibromatosis type 1, with a 2.0 cm tumor in the left submandibular gland and a metastatic lymph node [12]. These cases are human, but the anatomic principles transfer: the gland's location near the marginal mandibular nerve and the deep neck vessels makes resection technically demanding.

A systematic review and meta-analysis of gland-preserving surgery versus total gland excision for benign submandibular tumors found that gland-preserving surgery was associated with better preservation of unstimulated saliva flow at six months (mean difference 0.32 mL/min) and twelve months (mean difference 0.24 mL/min), shorter operative duration, reduced intraoperative blood loss, and lower risk of marginal mandibular nerve injury [13]. This evidence supports the general principle that preserving gland function, when oncologically safe, benefits the patient.

Common mistakes students make

The most frequent error is confusing the submandibular gland with the mandibular lymph node, especially in cats. The lymph node is rostral and ventral to the gland, is firmer and more discrete, and does not produce saliva when massaged. The second error is assuming that a swelling in the submandibular region is always glandular. It may be lymph node, salivary mucocele, abscess, or tumor. The third error is forgetting that the duct crosses the mylohyoid, so a surgical approach to the gland from the oral side will not reach the gland itself. The fourth error is treating a dilated duct as if it must contain a stone. Idiopathic megaducts exist and recur after treatment [6].

This article is educational and is not a substitute for veterinary diagnosis or treatment.

Quick Review

The submandibular gland sits in the submandibular triangle, bounded by the mandible, digastric muscle, and mylohyoid muscle.
Wharton's duct crosses the mylohyoid and opens at the sublingual caruncle beside the frenulum.
The gland is mixed seromucous and contributes most of the resting saliva.
In dogs, the mandibular gland is the dominant salivary gland.
In cats, the gland is closely related to the mandibular lymph node, so swelling here is often nodal.
In sheep the mandibular gland is larger than in goats, while the parotid is larger in goats.
Sialolithiasis and duct obstruction are the most common clinical problems, and not every obstruction is a stone.

Frequently Asked Questions

What is the submandibular gland?

The submandibular gland is a paired mixed seromucous salivary gland in the ventral neck that drains by Wharton's duct to the sublingual caruncle in the floor of the mouth.

Where does Wharton's duct open?

It opens at the sublingual caruncle, a small mucosal papilla beside the frenulum of the tongue.

Why is the submandibular gland the most common site for salivary stones?

Its duct is long, runs against gravity, and carries a more viscous mixed secretion, which favors stasis and mineral precipitation [8].

What is the difference between the submandibular gland and the mandibular lymph node in cats?

The lymph node is rostral and ventral to the gland, is firmer, and does not produce saliva when the gland is massaged.

Is the submandibular gland the same in all domestic species?

No. Its relative size, position, and duct course vary, and in dogs it is the dominant salivary gland while in ruminants the parotid contributes more ductal volume [3].

Can duct obstruction occur without a stone?

Yes. Idiopathic duct dilatation, or megaduct, occurs without lithiasis or stenosis and can cause recurrent swelling and discomfort [6].