416 Function of the two Ears in the Perception of Space. 



elucidated by observations made by and upon persons whose 

 hearing-power is abnormal. The author has had no opportu- 

 nities of making such observations. He has heard of one case 

 of interest — that of a gentleman stone-deaf of one ear from 

 infancy, and in whom the acoustic perception of direction was 

 almost wholly wanting. Xot only are experiments greatly 

 wanted upon semi-deaf persons, but also upon blind per- 

 sons, who usually have the acoustic perception of direction 

 abnormally acute. It would be still more desirable to have 

 observations made on a blind person deaf of one ear. 



It is also greatly to be desired that further experiments 

 should be made to determine the exact function of the pinna? 

 and of their complicated forms. The convolutions of the 

 pinna? differ markedly in different persons, and such differ- 

 ences must have some effect on the perception of sound. The 

 suggestion of Mach, that the convolutions have no direct 

 acoustic function in man, but that they represent the corre- 

 sponding structures which in animals serve to direct the 

 opening of the pinna? or to prevent them from beiug turned 

 inside out, is probably true, and is in conformity with the doc- 

 trine of descent, which accounts for many other inherited but 

 functionless appendages. Yet, if true, this does not affect the 

 truth of the statement that the convolutions, though destitute 

 of direct function, must still exercise some effect on the per- 

 ception of sound. In particular, it may be remarked that the 

 outer cartilaginous rim of the ear curves forward at the upper 

 part of the pinna, as if to catch sounds proceeding from below 

 the observer and in front of him. Is it possible that this 

 arises by natural selection from the fact that, on level ground, 

 sounds reach us more intensely from below, by reflexion from 

 the ground ? And is it not also connected with the fact that 

 persons who are partially deaf in both ears habitually throw 

 the head a little backward, so as to raise their line of sight 

 above the direction of the sound of the speaker's voice ? 



Whether the varieties of form of the pinna? eventually prove 

 to be of little or no importance in the question, there is an 

 ample field for observation for anatomists and physiologists in 

 the problems of the acoustical perception of space ; and it is 

 hoped that research in this department of physiological physics 

 will be facilitated by the attempt now made to lay down the 

 physical and experimental bearings of the question. 



