THE EAR. 



851 



lar branch of the pneumogastric ; the auriculo-temporal branch of the inferior 

 maxillary nerve ; the occipitalis minor from the cervical plexus, and the occipitalis 

 major or internal branch of the posterior division of the second cervical nerve. 

 The muscles of the pinna are supplied by the facial nerve. 



The Auditory Canal (rfieatus auditorius externus) extends from the bottom of 

 the concha to the membrana tympani (Fig. 457). It is about an inch and a half 

 in length if measui'ed from the tragus ; from the bottom of the concha its length 

 is about an inch. It forms a sort of S-shaped curve, and is directed at first inward, 

 forward, and slightly upward (pars externa) ; it then passes inward and backward 

 (pars media'), and lastly is carried inward, forward, and slightly downward (pars 

 internd). It forms an oval cylindrical canal, the greatest diameter being in the 

 vertical direction at the external orifice, but in the transverse direction at the 

 tympanic end. It presents two constrictions, one near the inner end of the carti- 

 laginous portion, and another, the isthmus, in the osseous portion, about three- 

 quarters of an inch from the bottom of the concha. The membrana tympani, 

 which occupies the termination of the meatus, is obliquely directed, in consequence 

 of which the floor of the canal is longer than the roof, and the anterior wall longer 

 than the posterior. The auditory canal is formed partly by cartilage and mem- 

 brane, and partly by bone, and is lined by skin. 



Cartilage of 

 the pinna' 



Promont. 



Cartilage of the ext. 

 auditory meatus 



FIG. 457. Transverse section of external anditory meatus and tympanum. Left side. (Gegenbaur.) 



The cartilaginous portion is about one-third of an inch (8 mm.) in length, it is 

 formed by the cartilage of the pinna, prolonged inward, and firmly attached to the 

 circumference of the auditory process of the temporal bone. 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 

 (incisurce Santorini), which extend through the cartilage in a vertical direction. 



The osseous portion is about two-thirds of an inch (16 mm.) in length, and 

 narrower than the cartilaginous portion. It is directed inward and a little forward, 

 forming a slight curve in its course, the convexity of which is upward and back- 

 ward. Its inner end, which communicates, in the dry bone, 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, except at its upper part, by a narrow 

 groove, the sulcus tympanicus, 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 downward. 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 (annulus tympanicus], incomplete at its upper part. See section on Osteology. 



