AUDITORY CANAL. 



631 



The Obliquus auris (Todd) consists of a few fibres extending from the upper 

 and back part of the concha to the convexity immediately above it. 



The arteries of the pinna are the posterior auricular, from the external carotid ; 

 the anterior auricular, from the temporal ; and an auricular branch from the occi- 

 pital artery. 



The veins accompany the corresponding arteries. 



The nerves are the auricularis magnus, from the cervical plexus ; the posterior 

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

 auriculo-temporal branch of the inferior maxillary nerve. 



The AUDITORY CANAL, meatus auditorius externus (fig. 313), extends from the 

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

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



Fig. 313. A Front View of the Organ of Hearing. Right Side. 



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, somewhat flattened from 

 before backwards, the greatest diameter being in the vertical direction at the ex- 

 ternal 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 this 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, being pro- 

 longed inwards to the circumference of the auditory process, to which it is firmly 

 attached. This tube 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 tympanum, is smaller 

 than the outer, and sloped, the anterior wall projecting beyond the posterior about 

 two lines ; it is marked, excepting at its upper part, by a narrow 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 



