CHAPTER XXIX 

 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 

 transformation of the sound waves into nerve stimuli which are 

 then transmitted through the path of the auditory nerve to the 

 cerebrum. 



THE EXTERNAL EAR 



The external ear includes an auricular or free portion and an 

 external auditory canal. 



THE AURICLE 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 occa- 

 sional 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 tis- 

 sue ; on the concave surface this union is very firm and permits but 

 little motion. The subcutaneous tissue, except in the lobule, con- 

 tains but little fat. 



THE EXTERNAL AUDITORY CANAL is divisible into an 

 outer cartilaginous and an inner bony portion ; the walls of the 

 two portions, except for this difference, are quite similar in struct- 

 ure. The cartilage is continuous with that of the auricle, and is 

 of the cellular elastic variety. The skin of this portion contains 

 large stiff hairs and both sebaceous and ceruminous glands. The 



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