THE EAR. 521 



while descending the scala tympani the vibrating perilymph 

 in the same is in direct contact with the basilar membrane 

 and at this point sets into vibrations, in a sympathetic way 

 already explained, the strings which are attuned to that 

 particular vibration. In other words, the human ear is but 

 the second tuning-fork set into motion by the first one. It 

 is the piano that responds again with the notes sung into it. 

 The student will have gone far in understanding the 

 exact manner of hearing when he has made clear to himself 

 the complete analogy of the basilar membrane to a musical 

 sounding-board on which are stretched as many as 3,000 

 differently attuned strings. It must be noticed further that 

 the proper vibrations of these strings is a purely physical 

 result, and would happen in a dead ear or an ear constructed 

 out of metal almost as readily as in a living ear. 



2. Rods of Corti. Standing on this basilar membrane 

 are two rows of rods which lean towards each other in such 

 a way as to form a tunnel underneath. These two series of 

 rods are called the rods of Corti. One series rests on the 

 basilar membrane just at the point where it is attached to 

 the lamina spiralis; the other, or outer rods, rest upon the 

 basilar membrane itself. The rods next to the lamina 

 spiralis, the inner rods, seem to be more slender and are 

 also more numerous than the outer rods, the numbers be- 

 ing about 6,000 and 4,500 respectively. 



At the base of the cochlea the rods of Corti are higher 

 but stand closer together than they do towards the top, 

 where they are lower and wider. (See Figure 161.) 



3. Reticular Membrane. Where the two sets of rods 

 meet there is attached a membrane which extends out 

 horizontally some distance over the basilar membrane. 

 This membrane is called the reticular membrane, the name 

 being derived from the fact that it is pierced with very many 

 small openings through which the hair endings of the audi- 

 tory cells beneath extend. 



