dental or alveolar) nerve, which supplies the bone and teeth up to the bicuspid region, where it bifurcates. The major portion of the nerve exits the mandibular body through the mental foramen and passes into and supplies the soft tissues of the chin and lower lip (2a). The smaller portion continues anteriorly within bone in the incisive canal toward the inferior aspect of the incisors (2b).

The fact that the mandibular canal bifurcates is often unclear radiographically. Nature being economical, the channels conducting the branches of the nerve are appropriate in size after bifurcation to the size of their respective neurovascular bundles. That portion arising from the mandibular canal and directed toward the mental foramen appears approximately the same size as the mandibular canal proper. The incisive canal is usually so much smaller in size than the mandibular canal, that the inferior dental neurovascular bundle appears to cease its course within bone at the mental foramen. In some cases, however, the incisive canal is quite distinct for a very short distance after the bifurcation. Then it rapidly narrows until it disappears near the midline.

Typically the mandibular canal is uniform in width — about 3 mm. or less — from the mandibular foramen to the mental fora-men. However, this dimension is often not consistent. Flared areas (3) may exist along the canal's course, or apparently compressed areas (4). These may be normal variations, and can usually be distinguished from pathological conditions by the presence of cortical bone at the canal margins, intact lamina dura in involved teeth and the absence of pain and other symptoms. Sometimes the difficulty in detecting an intact margin confuses the picture, and other diagnostic methods must be explored.

After entering the mandible at the mandibular foramen, the