CHAPTER XIX 

 THE EAR 



This organ may be subdivided for description into the external, 

 the middle, and the internal ear. The first two portions serve for the 

 collection and transmission of sound waves, the last for the transforma- 

 tion of the sound waves into nerve stimuli which are then transmitted 

 through the path of the acoustic nerve to the cerebrum. 



THE EXTERNAL EAR 



The external ear includes an auricular or free portion and an ex- 

 ternal acoustic (auditory) meatus. 



THE AURICLE 



The auricle, or pinna, contains a thin cartilaginous plate of peculiar 

 form which is covered on both sides by the skin. The cartilage is of 

 the elastic variety, but differs from the similar cartilages of other parts 

 in the abundance of its large cartilage cells; in occasional areas the 

 elastic reticulum is deficient. This reticulum is closely connected with 

 the fibrous perichondrium, beneath which it forms a complete layer. 

 The extrinsic muscles of the ear are inserted into the perichondrium 

 and the fibrous tissue by which it is surrounded. 



The skin of the external ear does not essentially differ from that 

 of other parts. It is supplied with fine hairs and with many large 

 sebaceous glands; sweat glands also occur on the outer surface. The 

 derma is united to the underlying cartilage by connective tissue; on 

 the concave surface this union is very firm and permits but little motion. 

 The subcutaneous tissue, except in the lobule, contains but little fat. 

 The lobule does not contain cartilage. 



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