September 18, 2018
Salivary glands play an important role at the entrance to the digestive system. We tend to take these structures for granted until something goes wrong. Too little saliva results in xerostomia, though this condition seems to be rare (or rarely diagnosed) in the species we treat. Abnormal accumulation of saliva results in formation of a sialocele, also referred to as a salivary mucocele. Hypersalivation can be due to primary salivary gland disease, but more commonly, it may be a sign of disease or pain elsewhere in the gastrointestinal tract. Often what is construed as “hypersalivation” is actually saliva being produced in normal amounts that is not being swallowed due to dysfunction or pain when swallowing.
There is minimal digestive enzyme (amylase) activity in saliva of cats and dogs. The primary function of saliva in cats and dogs is lubrication of food and protection of the oral mucosa. Saliva has antimicrobial properties and buffering agents. Evaporative heat loss in dogs is accomplished during panting.
The major and minor salivary glands work in concert to lubricate a bolus and begin the digestion process. Monostomatic glands deliver saliva to a distant site through a singular duct, whereas polystomatic glands produce saliva locally through multiple openings adjacent to the saliva-producing glands. In this month’s column, we will discuss the anatomy of the salivary glands. Knowledge of anatomy of the salivary glands is essential in deciding a surgical approach to a diseased gland. Other important structures, including nerves and vessels, are in close proximity to these structures. It is important to obtain knowledge of diseases of the salivary glands because not all salivary diseases are treated with surgery.
Parotid gland. The parotid gland is a V-shape gland surrounding the horizontal ear canal. The margins of the gland are indistinct because the gland is not surrounded by a capsule and it blends with subcutaneous fat and connective tissue of the muscles of the external ear. The parotid duct travels rostrally over the aponeurosis of the masseter muscle and opens into the mouth on a prominent papilla at the level of the maxillary fourth premolar tooth rostral to the zygomatic duct opening (Figure 1). Take care to avoid these ducts when raising a mucoperiosteal flap to extract caudal maxillary premolars and molars. Damage to the ducts can result in sialocele (mucocele) formation. The facial nerve lies deep to the gland and branches as it courses rostrally. The dorsal buccal branch of the facial nerve runs parallel to the duct dorsally, and the ventral buccal branch of the facial nerve travels parallel to the duct ventrally. The gland was once thought to be strictly a serous gland in dogs similar to people, but it is actually a mixed seromucous gland in dogs.
Mandibular gland. The mandibular salivary gland is a spherical structure ventral to the parotid gland and caudomedial to the mandibular (not “submandibular” as they are often incorrectly called) lymph nodes. The gland sits in the bifurcation of the external jugular vein, with the maxillary covering the caudodorsal aspect of the gland, and the linguofacial vein running along the ventral aspect of the gland. The mandibular duct runs rostrally between the mandible and the root of the tongue and opens into the mouth at the rostral-most opening of the sublingual caruncles. The mandibular gland is a mixed seromucous gland.
Sublingual gland. The monostomatic part of the sublingual gland shares a capsule with the mandibular gland and is intimately attached to the rostral surface of the mandibular gland. The polystomatic portion consists of multiple lobules located around the duct. The sublingual duct travels rostrally with the mandibular duct between the mandible and the tongue. The sublingual duct either opens as a separate opening caudal to the mandibular duct opening or joins with the mandibular duct, in which case there is only one opening at the caruncles. Both the monostomatic and polystomatic sublingual glands are mixed seromucous glands.
Zygomatic gland. The zygomatic gland is a mixed seromucous gland with an irregular shape that lies on the floor of the orbit ventral to the eye, immediately medial to the zygomatic arch. Several ducts, of which the most rostral is the largest, run ventrally and open on a fold of mucosa lateral to the maxillary first molar tooth. The maxillary artery, deep facial vein, and medial pterygoid muscle are located medial to the zygomatic gland.
We often envision salivary glands as focal structures with distinct capsules and ducts. In reality, glands not visible to the naked eye are present in the mouth throughout the labial, lingual, and palatal mucosa (Figure 2).
Cats have a fleshy, round, mixed seromucous polystomatic gland caudomedial to the mandibular first molar (Figure 3). Many a practitioner unfamiliar with this normal anatomical structure has biopsied it, thinking it was an oral mass.
1) Okuda A, Inouc E, Asari M. The membranous bulge lingual to the mandibular molar tooth of a cat contains a small salivary gland. J Vet Dent. 1996; 13(2): 61-64.
2) Eubanks DL, Woodruff KA. The basics of saliva. J Vet Dent. 2010; 27(4): 266-267.
Dr. John Lewis practices veterinary dentistry and oral surgery at NorthStar Vets in Robbinsville, N.J., and is the founder of Silo Academy Education Center in Chadds Ford, Pa.
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