Figure 1h. (a) Axial cross-sectional anatomy at the level of the skull base. Anatomic structures are shown on the left side of the diagram; spaces are shown on the right side. (b, c) Axial cross-sectional anatomy at the level of the upper maxillary antrum (b) and lower maxillary antrum (c). Anatomic structures are shown on the left side of the diagram; spaces are shown on the right side. CN = cranial nerve. (d, e) Axial cross-sectional anatomy at the level of the alveolar ridge (d) and mandible (e). Anatomic structures are shown on the left side of the diagram; spaces are shown on the right side. CN = cranial nerve. (f–h) Axial cross-sectional anatomy at the level of the C4 vertebra (f ), C6 vertebra (g), and C7 vertebra (h). Anatomic structures are shown on the left side of the diagram; spaces are shown on the right side.