102 The Ear 



When a tuning-fork in vibration is placed on the vertex of the 

 head of a person with healthy ears, and one external auditory meatus 

 is then blocked, the sound is best heard on that side, as dissipation of 

 the waves along the meatus is prevented, and they are, therefore, 

 echoed again and again from the tympanic membrane to the perilymph. 

 When the deaf ear of a patient cannot hear the tuning-fork so placed 

 the auditory nerve must be at fault. When the 'deaf ear hears 

 the vibrations better than the other there is probably obstruction of 

 either the external meatus or the Eustachian tube, and treatment 

 may be hopefully undertaken, for the auditory nerve is evidently 

 healthy. 



Development. The pinna is formed by the fusion of six small 

 tubercles upon the integument at the end of the first visceral cleft, 

 which is between the mandibular and hyoid arches. The fusion, how- 



Development of pinna from six tubercles. Supernumerary and persistent auricular 

 (After His.) nodules. (BLAND SUTTON.) 



ever, is never absolutely complete, for those tubercles from which the 

 tragus, anti-tragus, and the lobule are developed assert their indepen- 

 dence throughout life. Occasionally the fusion is extremely incom- 

 plete, supernumerary auricles and pendulous growths near the meatus 

 resulting. (For a Note upon DEVELOPMENT it. p. 123.) 



Sometimes the tragus-nodule is prevented from blending with the 

 elongated nodule just above it (from which the helix is formed) by 

 a recess of the epiblast which sinks between them and forms an 

 atiricular fistula. I saw such a case the other day, in which the in- 

 volution caused a fistula which ran beneath the superficial temporal 

 artery. From time to time it discharged a viscid secretion. It had 

 to be laid open and scraped out. (See also Trans. Soc. Med. Chir. 

 vol. Ixi.) Occasionally a similar fistula exists between the lower part 

 of the helix and the lobule, and sometimes the minute opening of one 

 of these fistulae becomes occluded, and the secretion collecting within 

 distends it into a dermoid cyst of pinna. 



Occasionally the tubercles are joined over the meatus in an elon- 

 gated or confused mass which represents the pinna ; this malforma- 



