STEUCTUEE OF THE PIXXA. 



741 



a little below the centre of the organ, is called the concha ; it surrounds the 

 entrance to the external auditory ineatus, and is unequally divided at its 

 upper part by a ridge, which is the beginning of the helix. In front of 

 the concha, and projecting backwards over the meatus auditorius, is a 

 conical prominence, the tragus, covered usually with hairs. Behind this, 

 and separated from it by a deep notch (incisura intertragica), is another 

 smaller elevation, the antitragus. Beneath the antitragus, and forming the 

 lower end of the auricle, is the lobule, which is devoid of the firmness and 

 elasticity that characterise the rest of the pinna. The thinner and larger 

 portion of the pinna is bounded by a prominent and incurved margin, the 

 helix, which, springing above and rather within the tragus, from the hollow 



Fig. 496. OUTER SURFACE OF THE PINNA OF THE EIGHT 

 AURICLE. | 



1, helix ; 2, fossa of the helix ; 3, antihelix ; 4, fossa 

 of the antihelix ; 5, antitragus ; 6, tragus ; 7, concha ; 

 8, lobule. 



Fu 



\ 



of the concha, surrounds the upper and posterior 

 margin of the auricle, and gradually loses itself in 

 the back part of the lobule. Within the helix is 

 another curved ridge, the antihelix, which, begin- 

 ning below at the antitragus, sweeps round the hol- 

 low of the concha, forming the posterior boundary 

 of that concavity, and is divided superiorly into 

 two diverging ridges. Between the helix and the 

 antihelix is a narrow curved groove, the fossa of 

 the helix (fossa iunominata, scaphoid ea) ; and in 

 the fork of the antihelix is a somewhat triangular 

 depression, the fossa of the antihelix (fossa triaugu- 

 laris vel ovalis). 



Structure. The pinna consists of a thin plat 3 of cartilage and of integu- 

 ment, with a certain amount of adipose tissue. It presents also several liga- 

 ments and small muscles of minor importance. 



The skin of the, pinna is thin, cbsely adherent to the cartilage, and con- 

 tains sebaceous follicles, which are most abundant in the hollows of the con- 

 cha and scaphoid fossa. 



The cartilage presents all the inequalities of surface already described as 

 apparent on the outer surface of the pinna ; and on its cranial surface exhi- 

 bits prominences the reverse of the concha and the fossa of the helix, while 

 between these is a depression in the situation of the antihelix. This cartilage 

 is not confined to the pinna, but enters likewise into the construction of the 

 outer part of the external auditory canal. When dissected separate from 

 other structures, it is seen to be attached by fibrous tissue to the rough and 

 prominent margin of the external auditory meatus of the temporal bone. 

 The tubular part is cleft in front from between the tragns and fore part of 

 the helix inwards to the bone, the deficiency being filled with fibrous inem- 

 "brane ; thus the cartilage may be said to be a plat^, a part of which assumes 

 the tubular form by being folded so as to bring the upper margin, which lies 

 in front of the tube of the ear, nearly into contact with the lower part, 

 which being coiled inwards upon itself forms the upper border of the tragus. 

 Following the free border of the plate backwards beneath the meatus, it is 

 seen to pass round the lower margin of the concha, and to form the promi- 

 nences of the tragus and antitragus, while the cartilage is absent altogether 



