THE EAR 



The organ of hearing is divided into three parts, namely, the 

 external ear, the middle ear, and the internal ear. 



External Ear. 



The external ear consists of the auricle, or pinna, and the meatus 

 auditorius externus. The auricle, or pinna, has been already 

 described (see Index). 



The external auditory meatus extends from the bottom of the 

 concha to the membrana tympani, and is about i inch in length. 

 It consists of two parts — outer, or cartilaginous, and inner, or 

 osseous. The cartilaginous part, which also consists of fibrous 

 tissue, is about J inch in length, and the osseous part, which lies 

 within the petrous portion of the temporal bone, is about § inch 

 long. The widest part of the meatus is its orifice, which is oval, the 

 long measurement being vertical. The narrowest part is situated in 

 its osseous portion, about i inch from the membrana tympani, and 

 it is known as the isthmus. There is another constriction of the 

 canal situated near the deep end of the cartilaginous part, and 

 produced by a projection which is placed antero-inferiorly. The chief 

 direction of the canal is inwards and slightly forwards. At first it 

 is also inclined upwards, then backwards, and finally downwards. 



The cartilaginous part is continuous with the cartilage of the 

 auricle, and is attached to the external auditory process of the 

 temporal bone. Its cartilage is folded so as to form a deep groove, 

 which is open at its upper and back part, the cartilaginous de- 

 ficiency being completed by fibrous tissue. The anterior wall of the 

 cartilaginous part presents two clefts, called the fissures of San- 

 torini, which are occupied by fibrous tissue. 



The osseous part has been described in connection with the 

 temporal bone. At its deep end there is a narrow groove, called 

 the sulcus tympanicus, which forms about five-sixths of a circle, 

 the deficiency being placed superiorly, at the notch of Rivinus, 

 where the ring is completed by the squamous part of the temporal 

 bone. The membrana tympani is set obliquely within the sulcus 

 tympanicus, being incHned downwards and towards the median 

 line. The floor and anterior wall of the meatus are consequently 

 longer than the roof and' posterior wall. 



The meatus is lined with skin, which is continuous with that of 

 the auricle. In the osseous part of the canal the skin is very thin, 

 and is provided with vascular papillae, but is destitute of glands 

 and hairs. It is reflected over the outer surface of the membrana 

 tympani, of which it forms the outer layer. In the cartilaginous 

 part of the canal the skin is thicker, and is provided with hairs, 

 connected with the follicles of which are sebaceous glands. In 



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