A 2) ld ee 
EXTERNAL AUDITORY MEATUS. 703 
average length, measured from the bottom of the concha, is about one ine ; 
(24 mm.), but, if measured from the level of the t1 ragus, nearly one inch and : 
half (35 mm.). Its 
anterior and inferior Pars ossea of external auditory meatus 
walls arelongerthan 
Crus antihelicis inferior 
the posterior and acetone - Cymba concha 
superior. The tube pean ak: Bet Gite halen 
Tel fs a ey Matleus 
consistsof two parts, Goahies 
viz.: (@)an external Cavum tympani 
fibro-cartilaginous Hopes 
portion, the pars 
cartilaginea, having Internal carotid —_ 
a length of about at 
8 mm.; and (6) an 
inter el osseous por- 
tion, the pars ossea, 
measuring = about 
16 mm., and formed 
by a portion of the aay ; 
temporal bone. The i Dili —V eNO TRANSVERSE SECTION or RIGHT EAR ; ANTERIOR HALE 
oops ey aes pe OF SECTION, viewed from behind (natural size). 
a somewhat S-shaped bend (Fig. 514) and may be divided into three portions, viz. : 
(1) pars externa, directed inwards, forwards, and shehtly upwards for about 7 mm. ; 
(2) pars media, inclining inwards and backwards for about 5 mm.; (3) pars interna, 
the longest of the three, passing forwards, inwards, and slightly downwards. On 
transverse section the canal is seen to be elliptical, its greatest diameter having an 
inclination downwards and backwards. Widest at its outer extremity, it becomes 
somewhat narrower at the inner end of the pars cartilaginea ; once more expanding 
in the outer part of 
Pars ecartilaginea of 
external auditory meatus 
Cavum conch 
Lower boundary of 
incisura intertragica 
Umbo i 
\ the pars ossea, it 1s 
. again constricted near 
+ ny part of 1 : 3 
Condyle of jaw Husteshian Hn the inner end of the 
Parotid gland i amalcarotidy  \ latter, where its nar 
:*_Membrana tympani rowest part, or isthmus, 
a is found at a distance of 
about 19 mm. from the 
bottom of the concha. 
The inner extremity 
sete Taig calle of the meatus is nearly 
circular and is closed 
by the membrana 
—TWateral sinus tympani. 
The lumen of the 
pars cartilaginea is in- 
Fic. 514.—HorizonraL SECTION THROUGH RicHT Ear; Upper Har or fluenced by the ONS 
SECTION, seen from below (natural size). ments of the lower Jaw, 
being increased when 
it is depressed. This can be easily verified by inserting a finger into the meatus, 
and then alternately opening and shutting the mouth. . 
The condyle of the jaw lies in front of the pars ossea, while between the jaw and 
the pars cartilaginea there intervenes a portion of the parotid gland. Below the 
meatus is the retro-mandibular part of the parotid gland. Behind the pars ossea, 
and separated from it by a thin plate of bone, are the mastoid air-cells. 
Structure of the Meatus,—The cartilage of the meatus, directly continuous 
with that of the pinna, is folded on itself to form a groove, opening upwards and 
backwards, the margins of which are connected by fibrous tissue. The inner end of 
the cartilage i 1s firmly fixed to the outer margin of the bony meatus, whilst its outer 
extremity is continuous with the cartilage of the tragus (vide p. 701). A couple of 
fissures, the fissures of Santorini, exist in “the anterior portion of the cartilage of the 
Tragus 
Cavum tympani 
Concha — ie 
