684 HANDBOOK OF PHYSIOLOGY. 



laris into the fenestras of which the tops of the various rods and cells 

 are received. When viewed from above, the organ of Corti shows a 

 remarkable resemblance to the key-board of a piano. In close relation 



II 



Fig. 404. Vertical section of the organ of Corti from the dog. 1 to 2, Homogeneous layer 

 of the so-called membrana basilaris; u. vestibular layer; v, tympanal layer, with nuclei and 

 protoplasm; a, prolongation of tympanal periosteum of lamina spiralis ossea: e, thickened 

 commencement of the membrana basilaris near the point of perforation of the nerves h; d, 

 blood-vessel (vas spirale) : e, blood-vessel: /, nerves: g. the epithelium of the sulcus spiralis 

 internus ; t, internal or tufted cell, with basil process k, surrounded with nuclei and protoplasm 

 (of the granular layer), into which the nerve-fibres radiate; I. hairs of the internal hair-cell; n, 

 base or foot of inner pillar of organ of Corti; m, head of the same uniting with the correspond- 

 ing part of an external pillar, whose under half is missing, while the next pillar beyond, o. pre- 

 sents both middle portion and base; r s d, three external hair-cells; t. bases of two neighboring 

 hair or tufted cells: .r. so-called supporting cell of Hensen: ?r, nerve-fibre terminating in the first 

 of the external hair-cells; J I to /, lamina reticularis. X 800. (Waldeyer.) 



with the rods of Corti and the cells inside and outside them, and proba- 

 bly projecting by free ends into the little tunnel containing fluid (roofed 

 in by them), are filaments of the auditory nerve. These are derived 

 from the cochlear division already mentioned. This passes up the axitf 

 of the cochlea, and in its course gives off fibres to the lamina spiralis. 

 These fibres are thick at their origin, but thin out peripherally, and 

 containing bipolar ganglion cells form the ganglion spirale. Beyond 

 the ganglion at the edge of the lamina the fibres pass up and become 

 connected with the organ of Corti. 



THE PHYSIOLOGY OF HEARING. 



All the acoustic contrivances of the organ of hearing are means for 

 conducting sound. Since all matter is capable of propagating sonorous 

 vibrations, the simplest conditions must be sufficient for mere hearing; 

 for all substances surrounding the auditory nerve would stimulate it. 

 The whole development of the organ of hearing, therefore, can have for its 

 object merely the rendering more perfect the propagation of the sono- 

 rous vibrations, and their multiplication by resonance; and, in fact, the 

 whole of the acoustic apparatus may be shown to have reference to these 

 principles. 



The external auditory passages influence the propagation of sound 



