orly and superficially to the artery. In this region the labial and cheek veins (10) join the facial vein. Several other venous branches, including the mental (11) and infraorbital veins (12), anastamose with the facial vein. One of the more significant, particularly in the spread of infection, is the deep facial vein (13), which courses below the zygomatic process and joins the pterygoid venous plexus, which empties into the retromolar vein.

The anterior facial vein turns under the mandible in front of the masseter and posterior and superior to the facial artery. Immediately after turning under, it receives the submental vein (14) and the palatine veins (15), which drain the tonsils. Then the anterior facial vein joins the retromolar vein, forming the common facial — or facial — vein. The common facial vein runs downward and backward a short distance, and usually anastamoses with the internal jugular vein at the level of the hyoid bone.

The retromolar vein is also known as the posterior facial vein because of its position in relation to the common and anterior facial veins. The retromolar vein receives blood from those regions supplied, in the main, by the maxillary and superficial temporal arteries. Important to note in dentistry, the retromolar vein drains the pterygoid venous plexus.

The pterygoid venous plexus can receive infected material directly from the posterior teeth or posterior implant sites of both arches by way of the alveolar network, or indirectly as the blood shunts or rushes backward and forward in veins associated with the more anterior portions of the maxillary and mandibular alveolar ridges and upper and lower lips. Once within the plexus, the infected material can drain into the retromolar vein or spread slowly upward into the cavernous sinus, possibly causing cavernous sinus thrombosis, if untreated.

Nerve Innervations

Of prime importance in the mandible is the pathway of the mandibular branch of the trigeminal nerve and its accompanying vessels. The trigeminal, or fifth cranial (1) nerve, is mainly responsible for the cutaneous supply of the face and scalp. In addition, it provides motor innervation for the muscles of mastication. The major portion is sensory and gives rise to three divisions: opthalmic (2), maxillary (3), and mandibular (4). In the lower part of the face on each side, a branch of the trigeminal nerve

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