134 THE STRUCTURE AND LIFE OF BIRDS chap. 



A few more points must be mentioned. The bony 

 labyrinth has a second window of membrane, and this, 

 yielding, allows greater vibrations to be imparted to 

 the fluid. In the cochlea, are very peculiar cells, 

 called the rods or pillars of Corti, forming two rows all 

 along the spiral, in all from four to six thousand of 

 them. They lie upon the inside of the membranous bag, 

 following the line along which it comes into contact with 

 the wall of bone. They stand leaning on one another, 

 and rather remind one of the keys of a piano. There are 

 delicate hairs at their ends. It is possible that each 

 of these rods vibrates to a certain note and no other. 

 If you put on a table several tuning forks which have 

 different pitches, and if you set vibrating another, 

 then if one of those on the table is of the same pitch, 

 it also will vibrate. The rest will be motionless and 

 silent. So these rods of Corti have been thought to 

 respond each to a certain note. In the labyrinth 

 there are no similar cells, and it has been suggested 

 that the membrane there is sensitive only to noise as 

 distinguished from music. 



It is not known exactly to what part of the brain 

 the nerve of hearing leads — i.e. where we have con- 

 sciousness of sound. 



The ear has two openings, the external one with 

 which every one is familiar, and another through what is 

 called the Eustachian tube to the mouth (E). The 

 two tubes from either ear unite and open into the 

 roof of the mouth just behind the two openings from 

 the nasal passages. 



I must now describe the main differences between 

 the human ear and the bird's. 



