352 HEARING. LECT. XIX. 



essential that all should vibrate in unison with the primitive 

 note, in order that the sound should be increased. 



In animals in which the pinna is moveable, the analogy 

 of this part of the ear with the ear-trumpet is very evident. 

 Thus we see the animal, when pursued, direct the opening 

 of the pinna backwards ; and, on the contrary, when pur- 

 suing its prey, it turns the same part forwards. In man 

 these movements are wanting ; and the external form of his 

 ear is also very different from that of other animals. Hence, 

 it is difficult for us to understand the use of the pinna, and 

 we might quote a number of instances in which hearing 

 has been but very slightly affected by its absence. Con- 

 sidering man's usual position, and the mobility and ele- 

 gance of his head, it does not appear possible to endow 

 the pinna with the power of motion without giving to this 

 organ the shape of an ear-trumpet; and all of you I suspect, 

 would be shocked at the idea of being thus transformed into 

 a kind of mythological monster. Let us add, that for the 

 same reasons, the pinna could not be mobile. So far from 

 this, it is formed of an elastic cartilage, the plane of which 

 is for the most part parallel to that of the membrane of the 

 tympanum ; and, consequently, normal to the axis of the 

 external auditory passage. According to the laws of the 

 propagation of vibratory movements, this is the best ar- 

 rangement it could have for receiving the sonorous undula- 

 tions, which, thus striking this membrane perpendicularly, 

 are propagated more readily into the interior of the ear, 

 either by the solid walls of the auditory passage, or by the 

 column of air which it contains. It is well known that 

 when we wish to hear distinctly, we place the head in such 

 a position that the pinna receives the sonorous waves nor- 

 mally. By the vibrations which sound excites in the ex- 

 ternal membrane of the ear, or by those produced in the 

 column of air contained in the auditory passage, the vi- 



