SURGICAL ANATOMY OF THE EAR. 867 



bottom of the internal auditory meatus, into two branches, the cochlear and 

 vestibular. 



The vestibular nerve, the posterior of the two, presents, as it lies in the internal 

 auditory meatus, a ganglion, the ganglion of Scarpa ; it divides into three 

 branches which pass through minute openings at the upper and back part of the 

 bottom of the meatus (area vestibular superior), and, entering the vestibule, are 

 distributed to the utricle and to the ampulla of the external and superior semicir- 

 cular canals. 



The nervous filaments enter the ampullary enlargements opposite the septum 

 trans versum, and arborize around the hair-cells. In the utricle and saccule the 

 nerve-fibres pierce the membrana propria of the maculae, and end in arborizations 

 round the hair-cells. 



The cochlear nerve gives off the branch to the saccule, the filaments of which 

 are transmitted from the internal auditory meatus through the foramina of the 

 area vestibularis inferior, which lies at the lower and back part of the floor of the 

 meatus. It also gives off the branch for the ampulla of the posterior semicircular 

 canal, which leaves the meatus through the foramen singulare. 



The rest of the cochlear nerve divides into numerous filaments at the base of 

 the modiolus ; those for the basal and middle coils pass through the foramina in 

 the tractus foraminosus, those for the apical coil through the canalis centralis, and 

 the nerves bend outward to pass between the lamellae of the osseous spiral lamina. 

 Occupying the spiral canal of the modiolus is the ganglion spirale, consisting of 

 bipolar nerve-cells, which really constitute the true cells of origin of this nerve, 

 one pole being prolonged centrally to the brain and the other peripherally to the 

 hair-cells of Cord's organ. Reaching the outer edge of the osseous spiral lamina, 

 they pass through the foramina in the labium tympanicum, and end, some by 

 arborizing around the bases of the inner hair-cells, while others pass between 

 Corti's rods and through the tunnel, to terminate in a similar manner in relation 

 to the outer hair-cells. 



Surgical Anatomy. Malformations, such as imperfect development of the external parts, 

 absence of the meatus, or supernumerary auricles, are occasionally met with. Or the pinna may 

 present a congenital fistula which is due to defective closure of the first visceral cleft, or rather 

 of that portion of it which is not concerned in the formation of the Eustachian tube, tympanum, 

 and meatus. The skin of the auricle is thin and richly supplied with blood, but in spite of this 

 it is frequently the seat of frost-bite, due to the fact that it is much exposed to cold, and lacks 

 the usual underlying subcutaneous fat found in most other parts of the body. A collection of 

 blood is sometimes found between the cartilage and perichondrium (licematoma awn's), usually 

 the result of traumatism, but not necessarily due to this cause. It is said to occur most fre- 

 quently in the ears of the insane. Keloid sometimes grows in the auricle around the puncture 

 made for earrings, and epithelioma occasionally affects this part. Deposits of urate of soda are 

 often met with in the pinna in gouty subjects. 



The external auditory meatus can be most satisfactorily examined by light reflected 

 down a funnel-shaped speculum ; by gently moving the latter in different directions the 

 whole of the canal and membrana tympani can be brought into view. The points to be noted 

 .ire. the presence of wax or foreign bodies, the size of the canal, and the condition of the mem- 

 brana tympani. The accumulation of wax is often the cause of deafness, and may give rise to 

 very serious consequences, causing ulceration of the membrane and even .absorption of the bony 

 wall of the canal. Foreign bodies are not infrequently introduced into the ear by children, and, 

 when situated in the first portion of the canal, may be removed with tolerable facility by means 

 of a minute hook or loop of fine wire, with reflected light; but when they have slipped beyond 

 the narrow middle part of the meatus, their removal is in no wise easy, and attempts to effect 

 it, in inexperienced hands, may be followed by destruction of the membrana tympani and possi- 

 bly the contents of the tympanum. The calibre of the external auditory canal maybe narrowed 

 by inflammation of its lining membrane, running on to suppuration ; by periostitis ; by polypi, 

 sebaceous tumors, and exostoses, The membrana tympani, when seen in a healthy ear, "reflects 

 light strongly, and, owing to its peculiar curvature, presents a bright spot of triangular shape at 

 its lower and anterior portion. ' ' From the apex of this, proceeding upward and slightly forward, 

 is a white streak formed by the handle of the malleus, while near the upper part of the mem- 

 brane may be seen a slight projection, caused by the short process of the malleus. In disease 

 alterations in color, lustre, curvature or inclination, and perforation must be noted. Such per- 

 forations may be caused by a blow, a loud report, a wound, or as the result of suppuration in 

 the middle ear. 



The upper wall of the meatus is separated from the cranial cavity by a thin plate of bone ; 



