THE INTERNAL EAR 



747 



The nerves terminate in essentially the same way in the sacs of the 

 vestibule and the ampullae of the semicircular canals. At the points 

 where the nerves enter, in addition to the otoliths, are cylindrical cells 

 of various forms, which pass gradually into the general endothelium of 

 the cavities. In addition to these cells, are fusiform nucleated bodies, 

 the free ends of which are provided with hair-like processes, called fila 

 acustica. These are about -%^-Q of an inch (31 /^) in length and are dis- 

 tributed in quite a regular manner around the otoliths. The nerves form 

 an anastomosing plexus beneath the endothelium and terminate proba- 

 bly in the fusiform bodies just described as presenting the fila acustica 

 at their free extremities. In the sacs of the vestibule and in the 

 semicircular canals, nerves 

 exist only in the maculae 

 acusticae and the ampullae. 



The cochlear division 

 of the auditory nerve 

 breaks up into a number 

 of small branches which 

 pass through the foramina 

 at the base of the cochlea 

 in what is called the tractus 

 spiralis foraminulentus. 

 These follow the axis of 

 the cochlea and pass in 



their rotirse toward the Fi %' ^^- Distribution of the cochlear nerve in the spiral 

 iru me lamina ^ The cochlea is from the right side and is seen from its 

 apex, between the plates antero-inferior part (Sappey). 



of the bony Spiral lamina. I, trunk of the cochlear nerve; 2, 2, 2, membranous zone 



^ , ,. of the spiral lamina ; 3, 3, 3, terminal expansion of the cochlear 



.between these plates OI nerve, exposed in its whole extent by the removal of the supe- 



rior plate of the lamina spiralis ; 4, orifice of communication 

 of the scala tympani with the scala vestibuli. 



bone, the dark-bordered 

 nerve-fibres pass each one 

 through a bipolar cell, these cells together forming a spiral ganglion 

 known as the ganglion of Corti. Beyond this ganglion the nerves form 

 an anastomosing plexus and finally enter the quadrilateral canal, or the 

 canal of Corti. As they pass into this canal they suddenly become pale 

 and exceedingly fine. They probably are connected finally -with the 

 organ of Corti, although their exact mode of termination has not yet 

 been determined. The course of the nerve-fibres to their distribution 

 in the cochlea is shown in Fig. 194. 



Organ of Corti. In the quadrilateral canal, bathed in the endolymph 

 throughout its spiral course, is an arrangement of pillars, or rods, 

 which are regular, like the strings of a harp in miniature. These are 

 the pillars of Corti. These pillars are external and internal, with their 



