706 



THE SENSES 



base of the lamina where they form the spiral ganglion. The nerve fibers 

 from the ganglion cells pass out through small holes in the periphery of the 

 spiral plate of bone, to enter the organ of Corti. Here they form small 

 longitudinal bundles that quickly end about the hair cells. 



THE SENSE OF HEARING. 



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

 ducting sound. Since all matter is capable of propagating sonorous vibra- 

 tions, the simplest conditions must be sufficient for mere hearing; since all 

 substances surrounding the auditory apparatus would stimulate it. The 

 complex development of the organ of hearing, therefore, must have for its 



mcmbrana lectori* 



outer hair-cells 







inner rod vas basilar outer cells of Deiters 

 membrane rod 



nerve fbrc* 



FIG. 438. Semidiagrammatic Representation of the Organ of Corti and Adjacent 

 Structures. (Merkel-Henle.) a, Cells of Hensen; b, cells of Claudius; c, internal spiral 

 sulcus; x, Nuel's space. The nerve fibers (dendrites of cells of the spinal ganglion) are 

 seen passing to Corti's organ through openings (foramina nervosa) in the bony spiral 

 lamina. The black dots represent longitudinally running branches, one bundle lying to 

 the inner side of the inner pillar, a second just to the outer side of the inner pillar within 

 Corti's tunnel, the third beneath the outer hair cells. 



object the more effective propagation of the sonorous vibrations and their 

 intensification by resonance; and, in fact, the whole of the acoustic apparatus 

 may be shown to have reference to these principles. 



The external ear and the auditory passages influence the propagation of 

 sound to the tympanum by collecting from the atmosphere the sonorous 

 undulations that strike against the external ear and by transmitting them by 

 the air in the passage to the membrana tympani. 



In animals living in the atmosphere, the sonorous vibrations are con- 

 veyed to the auditory epithelium through three different media in series; 

 namely, the air of the external ear and meatus, which sets in vibration the 

 tympanic membrane, the solid chain of auditory ossicles, and the fluid of the 

 labyrinth. Sonorous vibrations are imparted too imperfectly from air to 



