CHAPTER XV. 

 THE ORGAN OF HEARING. 



The organ of hearing consists of three portions, 

 external, middle, and internal ear, the last being the 

 essential part, as within this are the peripheral termi- 

 nations of the auditory nerve. 



i. The External Ear. The pinna or auricle pro- 

 jects from the side of the head and is covered with a 

 thin layer of skin, in which are found hairs, sebaceous 

 glands, and sweat glands. A cartilage matrix of 

 this portion is of the elastic variety with interposed 

 areas of non-elastic cartilage. The lower lobe is free 

 from cartilage and is composed of adipose tissue. 

 The external auditory meatus is the passage leading 

 inward from the concha as far as the tympanic mem- 

 brane. Its average length is about one inch. This 

 tube may be divided into an external cartilaginous 

 portion and an internal osseous portion. The skin 

 lining the cartilaginous portion is clothed with coarse 

 hairs and possesses modified sweat glands called 

 ceruminous glands. These are branched, of the 

 tubulo-alveolar variety, and empty into hair fol- 

 licles near the surface of the skin, or on the surface 

 of the skin in the neighborhood of the hair follicles. 

 The skin of the osseous portion is supplied with 

 neither hair nor glands, but possesses slender papillae. 



437 



