64 



VEKTEBRATA : MAMMALIA. 



liquid are suspended membranous pouches also filled with 

 a liquid, and in these are the terminating filaments of the 

 acoustic nerve or nerve of hearing. 



We may now understand how hearing is secured. The 

 vibrations of the air are collected by the external ear, and 

 conducted by the auditory tube to the drum or tympanal 

 membrane ; the vibrations of the drum are communicated 



an 



Eu ct mt ac I 



Auditory apparatus of the highest Mammal Man. 



a, external car; I, lobe of the ear; c, concha; ae, auricular canal; mt, membrana 

 tympani or drum; ct, cavity of the tympanum; o, opening iu wall of the tympanum; 

 (the fenestra ovalis and rotunda are near this opening); Eu, Eustachian tube; v, ves- 

 tibule; sc, semi-circular canals; co, cochlea; an, acoustic nerve. 



to the chain of little bones, and by these to the internal ear, 

 where they act upon the nervous filaments, which receive 

 the impression and convey it to the brain through the au- 

 ditory nerve. 



The nose is the organ of smell. In the Mammals it 



