brachial plexus and the subclavian vein in the posterior triangle of the neck.

The superior deep nodes receive afferents from the superficial nodes such as the submandibular and submental and their efferents drain partly into the inferior deep cervical nodes and partly into the jugular trunk in the inferior part of the neck. The latter, a collecting duct, joins the venous drainage at the junction of the internal jugular and subclavian veins on the right side and the thoracic duct on the left side of the neck.

The lymphatics of the gums drain mainly into submandibular nodes whose efferents reach the nodes of the superior deep cervical group. The central parts of the lower lip, tip of the tongue and anterior floor of the mouth drain primarily into the submandibular nodes. However, part of this drainage is also to a single node of the superior deep crevical group situated on the internal jugular vein at the level of the cricoid cartilage. This node, designated as "the principal node of the tongue" (jugulo-omohyoid node), is primarily involved in infection and malignancies of the tip of the tongue.

The lymph drainage of the dental pulp and periodontal ligament of the mandible follows in general the venous drainage of the alveolar canals. It is not possible to correlate a certain tooth with any special lymph node. Anterior teeth drain anteriorly through the mental foramina. However, the mandibular incisors drain directly into the submental nodes. The molars drain posteriorly through the mandibular canals. The premolars complicate the plan by draining both ways. The last molar can drain directly into the superior deep cervical nodes or through the mandibular canal into the submandibular nodes. A brief summary of the lymph drainage of the mandible is as follows:

The lymph from all mandibular teeth except the incisors first reaches the submandibular nodes. The incisors drain into the sub-mental nodes and the last molars may drain directly into the superior deep cervical nodes. Afferents from the submandibular and submental nodes reach the superior deep cervical nodes, the efferents of which converge on the jugular trunk partly by way of the posterior deep cervical nodes. Ultimately the right and left jugular ducts which drain the head and neck join the venous system at the confluencies of the internal jugular and subclavian veins.

—Ormond Mitchell, Ph.D.

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