828 



THE ORGANS OF SENSE. 



lost in the upper part of the lobule. Near the point where the helix begins 

 to descend a small tubercle, the tuberculum auriculae (Darwini), is often seen. 



Tympanic cavity, with chain of ossicles In fr0nt f the de ~ 



scending part of the 

 helix is a second ele- 



Auditory tube 



Membrana tympani 



Recessus epityrapanicus 



External acoustic meatu^ 



Single below, it 

 divides superiorly 

 into two limbs, 

 termed the crura 

 antihelicis, between 

 which is a triangular 

 Auricula depression, the fossa 

 triangularis. The 

 elongated furrow be- 

 tween the helix and 

 antihelix is named 

 the scapha. The con- 

 cavity of the concha 

 is overlapped in front 

 by a tongue-like pro- 

 cess, the tragus, and 

 below and behind by a 

 FIG. 703. DIAGRAMMATIC VIEW OF THE ORGAN OF HEARING. triangular projection, 



the antitragus ; the 



notch, directed downwards and forwards between these two processes, is named 

 the incisura intertragica. The tragus consists really 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 is situated below the 

 incisura intertragica, and is the 

 most dependent part of the 

 auricle. 



The medial or cranial surface 



also is irregular, and presents cms antihelicis superior- 

 elevations corresponding to the 

 depressions on its lateral surface, 

 e.g. eminentia conchas, eminentia 

 triangularis, etc. 



Fossa triangularis 



Crus antihelicis inferior 

 Cymba conchae 



Crus helici 



Incisura intertragica 



Tragus 



Antitragus 



Lobule 



FIG. 704. VIEW OF LATERAL SURFACE OF LEFT AURICULA 

 (half natural size). 



The auricula is usually smaller and 

 more finely modelled in the female than 

 in the male, but presents great varia- 

 tions in size and shape in different indi- 

 viduals. In the newly born child its 

 length is about one -third of that of the 

 adult, while it increases slightly in 

 length and breadth in old age. 



The relation of the width to the 

 height is termed the auricular index, and is expressed as follows : 



width of auricula x 100 



; TT- ^ : i = Auricular index. 



length of auricula 



This index is less in white than in dark races. 



The cephalo-auricular angle may be practically absent, as in those cases where the skin of the 

 head passes directly on to the lateral surface of the auricula, or it may be increased to nearly a 

 right angle, so that the lateral surface of the auricula looks directly forwards. The tuberculum 

 auriculae, the significance of which was recognised by Darwin, is a somewhat triangular 

 prominence which projects forwards in cases where the helix is well rolled over, but backwards and 

 upwards when the incurving of the helix has been arrested. More frequently present in men 

 than in women, it is of developmental interest since it has been shown to be well marked at the 

 sixth month of foetal life, the entire auricula, at this stage, resembling in appearance that of the 

 adult macaque monkey. 



The lobule may be small and sessile or considerably elongated ; it may adhere to the skin of 

 the cheek (i.e. webbed), or may tend to bifurcate at its lower extremity. 



