MIXUTE STRUCTURE OF THE COCHLEA. 763 



recently been generally misconceived. The history of the discovery and subsequent 

 appreciation of the nature of the canalis membranacea is fully given by Reichert. 

 (Abhandl. d. Konigl. Akad. d. Wissensch., Berlin, 1864.) 



Cochlear division of the auditory nerve. The nerve of the cochlea is 

 shorter, flatter, and broader than any of the other nerves of the internal 

 ear, and perforates the bone by a number of foramina at the bottom of 

 the internal rneatus, below the opening of the Fallopian aqueduct. These 

 foramina are arranged in a shallow spiral groove (tractus spiralis fora- 

 minulentus) in the centre of the base of the cochlea ; and they lead into 

 small bony canals, which follow first the direction of the axis of the cochlea, 

 through the modiolus, and then radiate outwards, between the plates of 

 the bony lamina spiralis. In the centre of the spiral groove is a larger 

 foramen which leads to the canalis centralis modiolL Through the central 

 foramen and straight canal the filaments for the last half-turn of the 

 lamina spiralis are conducted ; whilst the first two turns are supplied by 

 filaments which occupy the smaller foramina and bent canals. In the 

 bone the nerves have dark outlines, and near the edge of the spiral lamina 

 they form a plexus which contains ganglion-cells, and may be considered as 

 a spiral ganglion contained in an osseous canal, canalis spiralis modioli, 

 already mentioned. From the outer side of this ganglion the fibres, still 

 possessing the dark outline, pass onwards with a plexiform arrangement, and, 

 emerging from the bone beneath the labium tympanicum of the limbus, 

 are collected into bundles, which, opposite a line of perforations situated at 

 the junction with the membrana basilaris and named habenula perforata, 

 present the appearance of conical extremities entering those perforations. 

 Beyond this they have not yet been traced with certainty, although it seems 

 probable, as suggested by Kolliker, that the nerves are in continuity with 

 spindle-shaped cells in the organ of Corti. 



Microscopic structure. The limlus lamina spiralis is a thick structure 

 continuous with the periosteum of the vestibular surface of the osseous 

 lamina. Its free surface is thrown into a number of fungiform elevations 

 narrower at the base than at their extremities. Towards the inner part 

 of the limbus these elevations are short and vertical, but those which are 

 placed further out are more and more oblique and longer, and the labium 

 vestibulare is formed by the outermost of them, which are lengthened into 

 rib-like processes with flat extremities placed edge to edge, overhanging 

 the sulcus spiralis like teeth. In the spaces between the elevations numer- 

 ous small bodies like nuclei are disposed. In the floor of the sulcus 

 spiralis where the labium tympanicum is continued into the membrana 

 basilaris a series of elevations (apparent teeth of Corti) are directed into 

 the membrane, and between their outer extremities are the oblique perfora- 

 tions occupied by the conical extremities of the nerve-bundlea. This part 

 is the habenula perforata of Kolliker : it is described by him along with the 

 membrana basilaris, and by Henle along with the limbus. Henle considers 

 the appearance of elevations as caused merely by the nerve-bundles grooving 

 the under surface and leaving thicker structure between. 



The membrana basilaris is divisible into an inner and an outer zone. 

 The inner zone (habenula tecta vel arcuata) is covered over by the rods of 

 Corti ; the outer zone (zona pectinata) is attached peripherally to the walls 

 of the canal through the medium of the cochlear ligament. The inner 

 zone, together with the apparatus on its surface, continues, according to 

 Henle, of an uniform breadth of about -aj-oth of an inch, both in the dif- 

 ferent parts of the same cochlea, and likewise in different animals : so that 



