6. =Examination of the Ear.= The dura is removed from over the temporal bone and the _tegmen tympani_ cut off with chisel and hammer as indicated in Fig. 32, _1_, _2_, _3_, _4_, _5_, thus exposing the tympanic cavity as shown in Fig. 33. When the tegmen tympani is very hard and compact the hammer and chisel are used to remove that portion of the tegmen lying laterally to the eminence formed by the upper semicircular canals. As the ear-ossicles lie immediately beneath the roof of the tympanic cavity care should be taken not to injure them with the chisel, and this can be best accomplished by beginning to chisel so far posteriorly that the tegmen of the mastoid antrum is first cut away, and from this opening the cut is extended carefully until the tegmen tympani is removed. When the tegmen of the tympanic cavity is very thin and porcelain-like, as is often the case, it may be most quickly and expediently removed by means of the pointed bone-forceps. A complete view of the tympanic cavity is obtained by removing the coverings of the mastoid antrum posteriorly and the bony canal anteriorly after first drawing out the musc. tensor tymp. from the canal. The mastoid process may be opened with the saw or with chisel and hammer. The labyrinth may be exposed by cutting anteriorly with the chisel held horizontally in such a way as to spring off the upper half of the bony labyrinth, exposing the vestibule and cochlea. The superior and posterior semicircular canals come off, and from their open spaces the membranous semicircular canals can be lifted out with the forceps and then examined in water. The external auditory canal may be opened and the outer surface of the ear-drum examined by carrying the anterior flap of the scalp downward and forward until the entrance into the bony canal is reached. The external ear is then cut off close to the bone, using slight pressure so as to avoid tearing out the lining of the canal or injuring the tympanum. The anterior bony wall of the canal, and a part of the lower, are then carefully chiseled away until the membrane is exposed. Any bony projections on the thicker upper or lower wall of the canal may be trimmed off to give an unobstructed view. When pathologic changes are present upon any part of the wall of the canal the latter should be opened from the other side so as to expose the condition fully.