'LABYRINTHITIS 353 r. 181. Anatomical relations concerned in dealing with j labyrinth. 1, Horizontal part of canal for facial nerve; Lateral semicircular canal; 3, Superior vertical canal; Posterior vertical canal; 5, Bony wall of sigmoid sinus; Vertical portion of canal for facial nerve; 7, Oval ndow; 8, Anterior wall of bony meatus; 9, Promontory. Fig. 182. Neumann's labyrinth operation. After the radical mastoid operation has been completed, a further removal of bone in a medial direction opens up the posterior vertical canal. 'Y»V Fig. 183. Neumann's labyrinth operation. Still further removal of bone opens up the lateral or horizontal canal. Fig. 184. Neumann's operation. The smooth or medial end of the lateral canal is followed up into the vestibule, and, later, the pro- montory is removed by a gouge cut which joins the oval and round windows. The facial canal is seen intact between these two openings into the vestibule. the acute onset of symptoms follow a known chronic otitis media, or have been caused by injury during mastoid surgery, exploration of the labyrinth should be undertaken. There are two standard operations. Hinsberg's con- sists in performing a radical mastoidectomy, opening into the horizontal (lateral) semicircular canal, removing the stapes and opening the promon- tory. Neumann's is more radical in that it opens the two vertical semi- circular canals as well (Figs. 181-184).