THE EXTERNAL EAR. 



697 



auricular, from the facial'; the auricular branch of the pneumogastric; and the 

 auriculo-temporal branch of the inferior maxillary nerve. 



The Auditory Canal (Fig. 378), (meatus auditorius externus), extends from the 

 bottom of the concha to the membrana tympani. It is about an inch and a 

 quarter in length, its direction is obliquely forwards and inwards, and it is 



Fig. 378. A Front View of the Organ of Hearing. Eight Side. 



slightly curved upon itself, so as to be higher in the middle than at either 

 extremity. It forms an oval cylindrical canal, narrowest at the middle, some- 

 what flattened from before backwards, the greatest diameter being in the verti- 

 cal direction at the external orifice ; but, in the transverse direction, at the 

 tympanic end. The membrana tympani, which occupies the termination of the 

 meatus, is obliquely directed, in consequence of the floor of the canal being 

 longer than the roof, and the anterior wall longer than the posterior. The 

 auditory canal is formed partly by cartilage and membrane, and partly by 

 bone. 



The cartilaginous portion is about half an inch in length, being rather less 

 than half the canal; it is formed by the cartilage of the concha and tragus, 

 prolonged inwards, and firmly attached to the circumference of the auditory 

 process. The cartilage is deficient at its upper and back part, its place being 

 supplied by fibrous membrane. This part of the canal is rendered extremely 

 movable by two or three deep fissures (incisurse Santorini), which extend 

 through the cartilage in a vertical direction. 



The osseous portion is about three-quarters of an inch in length, and narrower 

 than the cartilaginous portion. It is directed inwards and a little forwards, 

 forming a slight curve in its course, the convexity of which is upwards and 

 backwards. Its inner end, which communicates with the cavity of the tympa- 

 num, is smaller than the outer, and sloped, the anterior wall projecting beyond 

 the posterior about two lines; it is marked, except at its upper part, 'by a nar- 

 row groove for the insertion of the membrana tympani. Its outer end is dilated, 

 and rough, in the greater part of its circumference, for the attachment of the 

 cartilage of the pinna. Its vertical transverse section is oval, the greatest 

 diameter being from above downwards. The front and lower parts of this 

 canal are formed by a curved plate of bone, which, in the foetus, exists as a 

 separate ring (tympanic bone), incomplete in its upper part. 



The skin lining the meatus is very thin, adheres closely to the cartilaginous 

 and osseous portions of the tube, and covers the surface of the membrana tym- 

 pani, forming its outer layer. After maceration, the thin pouch of epidermis, 

 when withdrawn, preserves the form of the meatus. The skin near the orifice 



