THE EAR. 449 



CHAPTER XV, 



OF THE EAR. 



THE organ of hearing is composed of three distinct parts, viz. 

 1. The exterior portion, which, although merely auxiliary, is 

 denominated the External Ear. 2. A chamber, situated in 

 the petrous portion of the temporal bone, which is called the 

 Cavity of the Tympanum. 3. A deeper seated cavity in the 

 same bone, which, from its complicated form, is denominated 

 the Labyrinth. 



Of the External Ear. 



The External Ear consists of the expanded portion, exterior 

 to the head, commonly called the Ear, and a wide tube passing 

 from it to the cavity of the tympanum, called Meatus Audito- 

 rious Externus. 



The form of the Ear is so familiar to every one, that it is 

 not necessary to describe it. The uppermost and longest por- 

 tion is denominated Pinna. The small pendulous part below is 

 called Lobus. 



The form as well as the firmness of the pinna, depends 

 entirely upon a cartilage: the lobus consists of skin and cellular 

 membrane. 



The skin which covers the pinna is particularly delicate ; 

 and, when the cuticle is separated from it by maceration, it 

 appears to be perforated with an unusual number of foramina, 

 which are the orifices of the sebaceous glands. It is connected 

 to the subjacent cartilage by a dense cellular membrane, which, 

 in most places, is free from adeps. 



The cellular membrane of the lobus contains adeps very 

 delicately arranged. 



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