If necessary, reflected light should now be used. To reach the exostoses it may be necessary, as in the previous case, to remove part of the posterior bony wall. With the gouge and mallet the exostoses are carefully chiselled away. They frequently abut on the tympanic membrane, so that their removal without injuring it may be well-nigh impossible. It is of the utmost importance that the field of operation should be kept dry, if necessary by repeatedly mopping out the canal with pledgets of cotton-wool soaked in adrenalin solution. The chief difficulty is to determine the situation of the tympanic membrane. A fine probe is used to discover any existing chink between the growths; this will be a guide to show the direction in which to work. As soon as a small passage has been made, sufficient to allow of a view of the deeper-lying parts, the ear should be syringed out and dried, and a thorough inspection made. The tympanic membrane can usually be seen as a greyish-blue membrane; at other times it can be recognized by touching it with a probe. After making certain of the position of the membrane, the rest of the operation is easy. A small seeker (Fig. 219), such as is used in the mastoid operation, is passed through the opening already made, and with it the deeper limits of the exostoses can be felt. The opening is gradually enlarged by removing the growths piecemeal with the chisel or gouge. Although the burr is contra-indicated when operating through the external meatus, it is frequently of great service in these cases in rendering the walls of the canal smooth. The disadvantages of using a burr are, that it is less easy to control (unless the surgeon has had considerable experience in using it), and that it destroys all the epithelial lining of the auditory canal with which it comes in contact. It should, therefore, only be used in those cases in which there is a complete ring of exostoses, but should be avoided if the exostoses are limited and if it is still possible to leave untouched a portion of the epithelial lining of the auditory canal. When the surgeon considers he has successfully removed the obstruction, he should verify this fact by syringing out and drying the ear, and again obtaining a clear view of the tympanic membrane. The fibrous portion is now replaced by inserting a finger into the cartilaginous meatus and pressing it back into the bony canal, the auricle being meanwhile pulled back into its normal position. The edges of the posterior wound are sutured together and the auditory canal is gently packed with gauze which should be inserted right down to the tympanic membrane. It is not necessary to make special meatal skin flaps, as careful packing of the auditory canal should be sufficient to keep the parts in apposition.