is attached to the mylohyoid line on the inner aspect of the mandible and therefore covers the medial surface of the lobe.
Figure 1.11 Superficial dissection of the left submandibular gland. The investing layer of the deep cervical fascia is elevated off the submandibular gland and the facial vein is identified.
The inferior surface, which is covered by skin, subcutaneous fat, platysma, and the deep fascia, is crossed by the facial vein and the cervical branch of the facial nerve which loops down from the angle of the mandible and subsequently innervates the lower lip. The submandibular lymph nodes lie between the salivary gland and the mandible. Sometimes one or more lymph nodes may be embedded within the salivary gland.
The lateral surface of the superficial lobe is related to the submandibular fossa, a concavity on the medial surface of the mandible, and the attachment of the medial pterygoid muscle. The facial artery grooves its posterior part lying at first deep to the lobe and then emerging between its lateral surface and the mandibular attachment of the medial pterygoid muscle from which it reaches the lower border of the mandible.
The medial surface is related anteriorly to the mylohyoid from which it is separated by the mylohyoid nerve and submental vessels. Posteriorly, it is related to the styloglossus muscle, the stylohyoid ligament, and the glossopharyngeal nerve separating it from the pharynx. Between these, the medial aspect of the lobe is related to the hyoglossus muscle from which it is separated by the styloglossus muscle, the lingual nerve, the submandibular ganglion, the hypoglossal nerve, and the deep lingual vein. More inferiorly, the medial surface is related to the stylohyoid muscle and the posterior belly of digastric.
Deep Lobe
The deep lobe of the gland arises from the superficial lobe at the posterior free edge of the mylohyoid muscle and extends forward to the back of the sublingual gland (Figure 1.12). It lies between the mylohyoid inferolaterally, the hyoglossus, and the styloglossus muscles medially, the lingual nerve superiorly and the hypoglossal nerve and deep lingual vein inferiorly.
Submandibular Duct
The submandibular duct is about 62 mm long and 3 mm in diameter in the adult. The wall of the submandibular duct is thinner than that of the parotid duct. It arises from numerous tributaries in the superficial lobe and emerges from the medial surface of this lobe just behind the posterior border of the mylohyoid. It crosses the deep lobe, passing upwards, and slightly backward for 5 mm before running forwards between the mylohyoid and hyoglossus muscles. As it passes forward, it runs between the sublingual gland and genioglossus to open into the floor of the mouth on the summit of the sublingual papilla at the side of the lingual frenum just below the tip of the tongue. It lies between the lingual and hypoglossal nerves on the hyoglossus. At the anterior border of the hyoglossus muscle, it is crossed by the lingual nerve. As the duct traverses the deep lobe of the gland, it receives tributaries draining that lobe.
Figure 1.12. Deep dissection of the left submandibular gland. With the submandibular gland retracted, the facial artery is identified in proximity to the facial vein.
Blood Supply and Lymphatic Drainage
The arterial blood supply arises from multiple branches of the facial and lingual arteries. Venous blood drains predominantly into the deep lingual vein. The lymphatics drain into the deep cervical group of nodes, mostly into the jugulo‐omohyoid node, via the submandibular nodes.
Nerve Supply to the Submandibular Gland
Parasympathetic innervation
The secretomotor supply to the submandibular gland arises from the submandibular (sublingual) ganglion. This is a small ganglion lying on the upper part of the hyoglossus muscle. There are additional ganglion cells at the hilum of the gland. The submandibular ganglion is suspended from the lingual nerve by anterior and posterior filaments (Figure 1.13).
Figure 1.13. Clinical photograph showing the relationship of the lingual nerve to the submandibular gland.
The parasympathetic secretomotor fibers originate in the superior salivatory nucleus and the preganglionic fibers then travel via the facial nerve, chorda tympani, and lingual nerve to the ganglion via the posterior filaments connecting the ganglion to the lingual nerve. They synapse within the ganglion and the postganglionic fibers innervate the submandibular and sublingual glands (Figure 1.9). Some fibers are thought to reach the lower pole of the parotid gland.
Sympathetic innervation
The sympathetic root is derived from the plexus on the facial artery. The postganglionic fibers arise from the superior cervical ganglion and pass through the submandibular ganglion without synapsing. They are vasomotor to the vessels supplying the submandibular and sublingual glands. Five or six branches from the ganglion supply the submandibular gland and its duct. Others pass back into the lingual nerve via the anterior filament to innervate the sublingual and other minor salivary glands in the region.
Sensory innervation
Sensory fibers arising from the submandibular and sublingual glands pass through the ganglion without synapsing and join the lingual nerve, itself a branch of the trigeminal nerve.
Sublingual Gland
EMBRYOLOGY
The sublingual gland arises in 20 mm embryos in the eighth week of intrauterine life as numerous small epithelial thickenings in the linguogingival groove and on the outer side of the groove. Each thickening forms its own canal and so many of the sublingual ducts open directly onto the summit of the sublingual fold. Those that arise within the linguogingival grove end up draining into the submandibular duct.
ANATOMY
The sublingual gland is the smallest of the major salivary glands. It is almond shaped and weighs approximately 4 g. It is predominantly a mucous gland. The gland lies on the mylohyoid and is covered by the mucosa of the floor of the mouth which is raised as it overlies the gland to form the sublingual fold. Posteriorly, the sublingual gland is in contact with the deep lobe of the submandibular gland. The sublingual fossa of the mandible is located laterally and the genioglossus muscle is located medially. The lingual nerve and the submandibular duct lie medial to the sublingual gland between it and the genioglossus.
Sublingual Ducts
The gland has a variable number of excretory ducts ranging from 8 to 20. The majority drain into the floor of the mouth at the crest of the sublingual fold. A few drain