A salivary gland is any cell or organ discharging a secretion into the oral cavity. A distinction is customarily made between the major salivary glands located some distance from the oral cavity and connected by extraglandular ducts, and the minor salivary glands which lie in the mucosa or submucosa, and open directly, or indirectly through a number many short ducts.
In humans, the major salivary glands are comprised of the paired parotids, and the submandibular and sublingual glands.

The paired parotid glands are the largest of the salivary glands. Each has an average weight of about 25 grams, and is an irregular, lobulated, yellowish mass, lying largely below the external acoustic meatus between the mandibleand sternocleidomastoid. The gland also projects forward on the surface of the masseter, where a small, usually detached part lies between the upper above zygomatic arch, and the parotid duct which lies below, the pars accessoria.
The parotid consists almost entirely of serous glandular tissue. Several structures traverse the gland in part, or in whole, and even branch within it. The external carotid artery enters the posteromedial surface, separating dividing into the maxillary artery, superficial temporal artery and the posterior auricular artery. The retromandibular vein, formed by the union of the maxillary and superficial temporal veins is superficial to the external carotid artery. The most superficial is the facial nerve, entering high on the posteromedial surface and passing forward and down behind the mandibular ramus in two main divisions, from which it's terminal branches diverge to leave by the anteriomedial surface passing medial to it's anterior margin.

About 5cm. long, this duct begins at the confluence of the two main tributaries within the anterior part of the gland, then crosses the masseter and at the anterior border turns medially at almost a right angle, traversing the corpus adiposum and the buccinator. It then runs a short distance obliquely forward between the buccinator and the oral mucosa to open upon a small papilla opposite the second upper molar crown. While crossing the masseter it receives the accessory parotid duct and it lies here between the upper and lower buccal branches of the facial nerve.
The wall of the parotid duct is thick, with an external fibrous layer containing smooth muscle and mucosa lined by low columnar epithelium. It's caliber is about 2mm., although smaller at it's oral orifice.

Vessels and nerves

The parotid artery is supplied by the external carotid and it's branches within and near the gland. The veins drain to the external jugular through local tributaries. The lymph vessels end in the superficial and deep cervical lymph nodes, interrupted by two or three nodes lying within and on the gland; The efferent innervation is autonomic, consisting of sympathetic fibers from the external carotid plexus and parasympathetic fibers which reach it via the tympanic branch of the glossopharyngeal nerve relaying in the otic ganglion and traveling along the auriculotemporal nerve.

Submandibular Glands:

The paired submandibular glands are irregular in shape and about the size of walnuts (10g.). Each consists of a large superficial duct, and a smaller deep part, continuous with each other around the posterior border of the mylohyoid. Although predominately serous, they are seromucous glands.

Submandibular Duct (Wharton's Duct):

This duct is about 5cm. long, and has a thinner wall than the parotid duct. It begins from numerous tributaries in the superficial part of the gland, and emerges from the medial surface of this part of the gland behind the posterior border of the mylohyoid. It traverses the deep portion, first passing up and slightly back for 4 or 5 mm., and then forward between the mylohyoid and hypoglossus. Then passing between the sublingual gland and the genioglossus, it opens into the floor of the mouth on the summit of the sublingual papilla at the side of the frenulum of the tongue. On the hypoglossus it lies between the lingual and hypoglossal nerve, it's terminal branches ascend on it's medial side.

Vessels and nerves:

The ramus mandibularis nerve passes through the superficial layer of the deep cervical fascia and is directly superficial to the gland. The hypoglossal nerve courses deep to the tendon of the digastric muscle and lies medial to the deep leaf of the deep cervical fascia. The facial artery courses medial to the posterior belly of the digastric muscle and then hooks over that structure to enter the submandibular gland, exiting at the inferior border of the mandibule at a point marked by the facial notch. The lingual artery courses along the lateral surface of the middle constrictor, deep to the digastric muscle, then runs anteriorly medial to the hypoglossus muscle.
The Lingual Nerve passes between the medial pterigoide muscle and ramus of the mandibule, entering the mouth just below the lower third molar and courses in a submucosal plane along the hyoglossus. Midway along that muscle it sends two branches to the submandibular ganglion. The parasympathetic nerve supply to the submandibular gland originates in the superior salivatory nucleus and travels via the nervus intermedius and chords tympani (which is carried by the lingual nerve in it's distal portion) to the submandibular ganglion. Some fibers synapse in the ganglion, and others synapse in the gland itself; The sympathetic supply to the submandibular gland is the same as for the parotid gland.