Anterior Neck Dissection

• The hyoid bone connects to the mandible via the mylohyoid muscle, which forms the floor of the mouth.
• The anterior belly of the digastric muscle lies superficially to the mylohyoid.
• The nerve to the mylohyoid and the submental branch of the facial artery are located between the mylohyoid and anterior belly of the digastric.
• The submandibular salivary gland and lymph nodes lie upon the mylohyoid, partially hidden under the mandible.
• The investing layer of deep cervical fascia covers these structures.
• The platysma muscle, anterior jugular veins, and submental lymph nodes are located in the subcutaneous tissue.
• The upper division of the transverse cervical nerve (C2) supplies the skin in this region.

Platysma

• The platysma is a broad, flat sheet of muscle that extends from the deep fascia over the upper part of the pectoralis major and the anterior deltoid to the lower border of the mandible.
• Some fibers reach the lateral lower lip by passing under the depressor anguli oris.
• The muscle covers the external and anterior jugular veins.
• The two platysma muscles converge towards the midline beneath the chin.
• The lateral border slants up across the parotid gland and converges into a triangle attached to the modiolus, forming the risorius muscle.
• The cervical branch of the facial nerve provides nerve supply.
• Afferent (proprioceptive) fibers run with the transverse cervical nerve.
• It plays a role in facial expression, assists mouth opening, raises cervical skin ridges during strenuous activity.
• During facelifts, it can be attached to the sternocleidomastoid behind the ear, with skin mobilized superficially to avoid nerve damage.

Anterior Jugular Veins

• These veins begin beneath the chin and run downwards beneath the platysma to the suprasternal region.
• They pierce the deep fascia and lie in the suprasternal space, often connected by an anastomotic vein.
• The veins angle laterally and pass deep to the sternocleidomastoid to drain into the external jugular vein.

Submental and Submandibular Lymph Nodes

• Three or four submental nodes lie beneath the chin, either superficial or deep to the investing layer of deep cervical fascia.
• They drain a wedge of tissue in the floor of the mouth opposite the lower incisor teeth, including teeth, gums, lip, and tip of tongue.
• Submental nodes drain to submandibular nodes or directly to the upper deep cervical group.
• Around six submandibular lymph nodes lie on the surface of the submandibular gland.
• They drain the submental nodes, lateral lower lip, upper lip, external nose, anterior tongue, anterior nasal walls, paranasal sinuses (frontal, anterior and middle ethmoidal, and maxillary), and all teeth except lower incisors.

Submandibular Fossa

• The submandibular fossa is deep to the investing layer of deep cervical fascia and the mandible's inferior border.
• The fascia attaches to the mandible's inferior border and the entire hyoid bone.
• It supports the submandibular gland and gives a very tenuous capsule around the deep surface of the gland.
• The fossa extends to the mylohyoid muscle, projecting upwards under the mandible to the mylohyoid line.
• Attachments of the mylohyoid muscle and the deep fascia limit swelling in the space.
• Distension of the space occurs in Ludwig's angina, a cellulitis usually due to infection spreading from teeth or tonsil).
• The nerve to mylohyoid branches from the inferior alveolar nerve at the mandibular foramen.
• It pierces the sphenomandibular ligament at its attachment to the inferior margin of the foramen. Accompanied by small branches of the inferior alveolar artery and vein.
• The vessels indent the mandible, forming the mylohyoid groove.
• The mylohyoid groove marks the upper limit of the attachment of the medial pterygoid muscle.
• The small artery supplies the periosteum and some fibers of the medial pterygoid.
• The nerve passes forwards on the neck surface of the mylohyoid muscle.
• The nerve ends between the anterior belly of digastric and mylohyoid, supplying both.
• The submental branch of the facial artery accompanies the nerve, perforating the mylohyoid to supply the anterior floor of the mouth, including the sublingual gland.
• Submental veins run back to the facial vein.
• Lymphatics pierce the anterior part of mylohyoid to drain the tongue's tip and floor of the mouth into the submental lymph nodes.

Submandibular Gland

• The submandibular gland is mixed mucous and serous in humans.
• It consists of a large superficial part and a small deep part, continuous around the posterior margin of the mylohyoid muscle.
• The superficial part fills the space between the mandible, mylohyoid, and investing layer of deep cervical fascia.
• The lateral surface lies against the submandibular fossa of the mandible, overlapping the front of the medial pterygoid insertion.
• The facial artery grooves the lateral surface posteriorly.
• The inferior (superficial) surface is covered by skin, platysma, and investing fascia.
• The facial vein, cervical branch of the facial nerve, and marginal mandibular branch of the facial nerve (if unusually low) cross the inferior surface.
• Submandibular lymph nodes lie in contact with and within the gland.
• The medial surface lies against the mylohyoid and its vessels, overlapping the hyoglossus, lingual nerve, submandibular ganglion, hypoglossal nerve, and deep lingual vein towards the back.
• The deep part of the gland extends forwards between the mylohyoid and hyoglossus, with the lingual nerve above and the submandibular duct and hypoglossal nerve below.
• The submandibular duct (of Wharton) 5 cm long.
• It emerges from the superficial part of the gland near the posterior border of the mylohyoid.
• It runs forwards between the mylohyoid and hyoglossus, then between the sublingual gland and geniohyoid, opening into the floor of the mouth beside the frenulum.
• Blood supply is from the facial artery, with veins draining into the facial vein.
• Lymph drains to the submandibular lymph nodes.
• Secretomotor fibers to the gland have cell bodies in the submandibular ganglion with some in ganglionic masses on the gland's surface.
• Preganglionic fibers pass from the superior salivary nucleus in the pons via the nervus intermedius, chorda tympani, and lingual nerve.
• Sympathetic (vasoconstrictor) fibers come from the plexus around the facial artery.
• During development a groove in the floor of the mouth becomes a tunnel, the blind end proliferates to form the secreting acini (ectodermal origin).
• The superficial part is easy to expose under the platysma, but the skin incision should be about 4 cm below the mandible, avoiding the marginal mandibular branch of the facial nerve.
• Removal requires ligation of the facial artery and vein above and below it.
• The gland is dissected away from the lingual nerve, with ligation of the duct as it lies on the hyoglossus.
• Removal of a stone from the duct is carried out intraorally by incising the duct over the stone; suturing is not required.

Anterior neck anatomy includes the hyoid bone connecting to the mandible via the mylohyoid muscle. The anterior belly of the digastric muscle lies superficially to the mylohyoid. The platysma muscle, anterior jugular veins, and submental lymph nodes are located in the subcutaneous tissue.