The Oral Cavity and the Oropharynx
The spatial relationships of the first and second cervical vertebrae, especially of the dens axis, to the facial region is of great help in posterior transoral surgery [1–2]. The first two cervical vertebrae are projected into the oral cavity when the mouth is opened. With the mouth closed, the body of the second vertebra corresponds to the level of the lower lip, the first vertebra to the upper lip, and the dens axis to the philtrum. The dens axis is normally inclined slightly backward at a 10° angle in relation to its body . The relationship of the dens axis to the skull base is clinically important. The position of the dens is determined by different lines (such as the bimastoid or Chamberlain’s line). The transverse process of the first vertebra can be asymmetrical and may be mistaken clinically for a tumor beneath the mastoid process (see Sects. 11.11, 1.15.2).
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