A Manual of Diseases of the Ear (Paperback)

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1893 Excerpt: ...tympanum it gives off small branch canals for the nerve to the stapedius and the chorda tympani. The position of the aqueduct and the delicacy of its covering on the tympanic oide expose the facial nerve to great danger during an accidental or intentional puncture of the membrane. This membrane consists of three layers (see Fig. 8), an external and internal, derived from the epidermal and mucous lining of the outer and middle ears respectively, and an intervening, composed of mixed white and elastic fibres. When chronic inflammation of the middle ear has thickened this threefold membrane, it offers considerable resistance to the passage of a knife. Under the gentle pressure of the operator's hand, however, it gives way suddenly, and, with a consequent jork, the point of the instrument may travel across the shallow cavity to impinge against, possibly to enter, the inner wall. Thus the facial nerve may perhaps be divided; but, if it escape immediate division, effusion of blood into its arachnoid sheath may cause impairment of its function. The signs of injury to the facial nerve--immediate or delayed--are unmistakable. The muscles of the corresponding side of the face being paralysed, the orbicularis palpebrarum is unable to close the eyelids; whilst, as the orbicularis oris and the buccinator are rendered useless, the food lodges in the pouch of the cheek, or, mixed with saliva, trickles out of the mouth. (As the last-named muscle obtains additional motor filaments from the third division of the 5th nerve, its paralysis on division of the facial is only partial.) The mouth, which was kept in position by antagonistic muscular forces, is now drawn over to the unaffected side. Impairment of taste on the affected side is a remarkable feature in injury to the fac...