VESSELS AND NERVES OF THE PINNA. 



77 



about 25 mm. long, but the superior and posterior boundaries are considerably 

 shorter than the inferior and anterior. If the part of the concha which is 

 bounded anteriorly and externally by the tragus is reckoned in with the canal, 



Fig. 85, DIAGRAMMATIC VIEW FROM 



BEFORE OF THE PARTS COMPOSING 

 THE ORGAN OF HEARING OF THE 



LEFT SIDE. (After Arnold. ) 



The temporal bone of the left side, 

 with the accompanying soft parts, has 

 been detached from the head, and a 

 section has been carried obliquely 

 through it so as to remove the front 

 of the meatus externus, half the 

 tympanic membrane, and the upper 

 and anterior wall of the tympanum 

 and Eustachian tube. The meatus 

 internus has also been opened, and 

 the bony labyrinth exposed by the 

 removal of the surrounding parts of 

 the petrous bone. 1, the pinna and 

 lobe ; 2 to 2', meatus externus ; 2', 

 membrana tympani ; 3, cavity of the 

 tympanum ; above 3, the chain of 

 small bones ; 3', opening into the 

 mastoid cells ; 4, Eustar.hian tube ; 

 5, meatus internus, containing the 

 facial (uppermost) and auditory 

 nerves ; 6. placed on the vestibule 

 of the labyrinth above the fenestra 

 ovalis ; a, apex of the petrous bone ; 6, internal carotid artery ; c, styloid process ; d, facial nerve 

 issuing from the stylo-mastoid foramen ; e, mastoid process ; /, squamous part of the bone. 



its length must be given as considerably more (35 mm ). In its inward course it is 

 inclined at first somewhat forwards and very slightly ascends (external portion) : it 

 then turns pretty sharply backwards and is nearly horizontal (middle portion), and 



fossa scaphoidca 



fossa i liter crur alls 

 concha proper (upper part) 



impression of membrana 

 flaccida 



bend of mcalus concha proper (lower part) 

 Fig. 86. CAST OF THE EXTERNAL AUDITORY MEATDS. (Bezold.) 



is finally directed slightly forwards and decidedly downwards (internal portion) 

 (fig. 85). The calibre of the passage is smallest in the osseous part of the canal a 

 few millimeters from the membrana tympani : it is also somewhat contracted near 

 the end of the cartilaginous portion. Its form and dimensions have been studied 

 by v. Bezold, chiefly by means of casts of the cavity : the results of the transverse 



