DEVELOPMENT OF THE OKGAN OF HEARING. 



53 



commonly seen between the tragus and root of the helix, or 

 between the antihelix and helix. The outgrowth of the ear may 

 be arrested at any stage. The mandibular part is supplied, as 

 one would expect from its origin, by the third division of the 5th, 

 while the sensory fibres of the hyoid part come from the 2nd 

 cervical by the great auricular and small occipital nerves. 



Darwin's Tubercle. — The human ear appears to be derived 

 from a form in which the margin was pointed at the posterior 

 superior angle, such as is seen in many of the lower forms of 

 apes and mammals generally. With the retrogression of the 

 posterior border or descending helix and increased development of 

 the antihelix in the human ear, the posterior margin became 

 infolded ; hence the tip appears as a tubercle on the inturned 

 posterior margin or welt of the human ear (Fig. 38). 



Muscles of the External Ear. — These are derived from the 



saccus endolymph, 



semicircular canal 



periotic capsule 

 otocyst (utricle) 



pharynx 



tympanum 



vein 



■facial nerue 

 antrum 



■chorda tympani 

 malleus 

 drum 

 ext. and. meatus 



tragus 



Fio 39 -Showing the condition of the Auditory Organs in a 6th week human foetus. 

 (After Siobenmann.) 



platysma sheet and are supplied by the nerve of that sheet— 

 the Vllth or facial. The ear muscles are not so reduced in man 

 as in some other primates, such as the orang. 



