Right lateral view of mastoid process, mastoid air cells, and external auditory canal. For orientation, the left border of the image is superior, the top border is anterior. The mastoid process has been drilled to reveal a honeycomb arrangement of air cells. The auricle has been removed for a view of the external auditory canal. The canal ends medially at the tympanic membrane. The stylomastoid foramen has been exposed and from it emerges the facial nerve. (Image courtesy of AL Rhoton, Jr.)