700 THE ORGANS OF SENSE. 
EXTERNAL EAR. 
The external ear ! includes—(@) the pinna or auricula, attached to and projecting 
from the side of the head; and (/) the passage or external auditory meatus (meatus 
acusticusexternus),lead- 
Tympanic cavity, with chain of ossicles 
Semicireular cana! ing inwards from the 
Basile most depressed part of 
Ductus endolymphaticus | 
the pinna as far as the 
tympanic membrane or 
outer wall of the middle 
ear, 
Saccule 
THE PINNA. 
The pinnaorauricula 
(Fig. 510) presents two 
surtaces, outer and inner, 
the latter forming an 
angle (cephalo-auricular 
angle) of about 30°, 
opening backwards, with 
the side of the head. 
The outer surface is 
irregularly concave, but 
j presents several well - 
marked elevations and 
depressions. Thedeepest 
of the depressions 1s 
situated near its middle, and is named the concha (concha auricule). It is divided 
by an almost transverse ridge, the crus helicis, into an upper, smaller, and a lower, 
larger portion: the former is termed the cymba conche ; the latter, which leads into 
the meatus, the cavum conche. 
Anteriorly, the crus helicis is con- (es 
tinuous with the margin of the {iy | 
pinna or helix, which is folded over, \ 
in the greater part of its extent, Crus antihelicis superior} 
like the rim of a hat, and is NESS MOL SSIES 
directed at first upwards, and then Crs eee ee 
backwards and downwards, to aati eee 
become gradually lost a ttle below 
the middle of the pinna. Where ‘Pragus 
Eustachian tube 
Membrana tympani | 
tecessus epitympanicus | 
External auditory meatus 
Fic. 509.—DIAGRAMMATIC VIEW OF THE ORGAN OF HEARING. 
-Helix 
Fossa 
scaphoidea 
»  Tuberculum 
superius 
ST 
Anti-helix 
4 Cavum 
conchee 
the helix begins to turn down- iatittanitecie: 9 
wards a small tubercle, the tuber- ~ Antitragus 
culum superius (Darwini), is often 
seen ; 1b will be again referred to. Lobule 
In front of the descending part of ie ger atieeae man even k 
the helix is a second elevation, Sn ana ot iiale ies ae OR ae 
the antihelix. Single below, this 
divides superiorly into two limbs, termed the crura antihelicis, between which is a 
triangular depression, the fossa of the antihelix, or fossa triangularis. The 
elongated furrow between the helix and antihelix is named the fossa of the helix 
or scapha. The concavity of the concha is overlapped in front by a tongue-like 
process, the tragus, and behind by a triangular projection, the antitragus. The notch, 
directed downwards and forwards between these two processes, is named the 
incisura intertragica. ‘The tragus really consists of two tubercles, the upper of 
which constitutes the tuberculum supratragicum of His, and is separated from the 
helix by a groove, the sulcus auris anterior. The lobule (Jobulus auricule) is 
' Although it is usual to speak of the external, middle, and internal ear, it would be more correct to 
use the terms external, middle, and internal portions of the ear. 
