alveolar crest or be right at it, the incision to reveal the ridge should be made lingual to the crest, within the zone of attached gingiva. The canal tends to run buccal to the crest, and offsetting the incision lingually should avoid interference with its contents.

If the inferior alveolar artery is severed accidentally and local pressure is not sufficient to stop profuse bleeding, pressure must be applied above the mandibular foramen, where the artery enters the ramus. Copious or continuous bleeding must be stopped by ligating the artery.

As for the incisive artery, its branches are little larger than dental arteries. They are usually so small that severing them does not necessitate measures to stop blood flow.

The lingual artery may originate at the external carotid artery above the superior thyroid at the level of the greater horn of the hyoid bone, or it may arise from a short trunk — the linguofacial trunk — which it shares with the facial artery. The lingual artery runs almost horizontally forward. As it approaches the tongue, it sends a branch to the hyoid bone and its attached muscles.

As the inferior alveolar artery passes through the mandibular canal, it sends branches into the marrow spaces of the bone toward the alveolar process. Some of these supply the teeth, entering their root canals through the apical foramina, and others supply the interdental and interradicular septa. As these arteries ascend, many small branches arise at almost right angles and supply the periodontal ligaments and eventually the gingiva. In the gingiva these twigs anastamose with superficial branches of the arteries supplying the oral and vestibular mucosa, richly providing these tissues with blood.

Of particular importance here is the diminishment of blood to the mandible when teeth are lost. Upon the loss of a tooth, the arteries supplying its pulp and periodontal membrane are no longer functional. Nature being economical, these tend to resorb, leaving only those arteries that supply living bone cells and the gingiva. In comparison with the maxillae, with their numerous nondental functions, the body of the mandible may become relatively poorly supplied with blood. The denser areas, and they are many, are typically poorly supplied initially, in accordance with their more static state. Upon tooth loss, a major source of blood, the dental arteries, diminish. Thus compared with other bones, the superficial parts of the mandible are not so freely supplied with blood. As the alveolar ridge is exposed and subjected to surgical trauma, it may necrose, particularly if the inferior alveolar

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