CHAPTER XXXIV. 



THE ORGAN OF HEARING. 



I. THE EXTERNAL AND MIDDLE EAR, EXCLUDING THE EUSTACHIAN TUBE. 

 BY J. KESSEL. 



IN the auditory organ of the more highly organised Vertebrata 

 we may distinguish a sound-conducting and a .sound-perceiving 

 apparatus. The conducting apparatus includes the external 

 and middle ear, whilst the sensory apparatus is contained 

 ID the vestibule, the semicircular canals, and the cochlea. 



a. THE EXTERNAL EAR. 



This is represented by the auricle or concha, the external 

 auditory meatus and the membrana tympani. 



AURICLE. The auricle, with the exception of the lobulus, is 

 essentially formed of elastic cartilage, the complex moulding of 

 which confers upon it its peculiar shape. The cartilage itself 

 belongs to the group of reticular cartilages ; it is from one to two 

 millimeters thick, and is invested by a perichondrium which 

 contains a large number of elastic fibres. The fibres penetrate 

 into the matrix of the cartilage, and form fine plexuses inter- 

 weaving with one another, in the meshes of which small cartilage 

 corpuscles are imbedded. (See Rollett, vol. i., p. 106, of this 

 Manual.) 



In regard to the muscles that are in connection with the 

 concha, only those need here be mentioned tha^t run between 

 its several regions. These are small thin striated muscles that 

 are inserted by means of short tendons into the perichondrium. 



The cutis of the concha, which is continuous with that of the 



