1490 



HUMAN ANATOMY. 



FIG. 1250- 



Concha 



External auditory canal 

 Membrana flaccida 

 Depression for 



malleus 



Umbo 

 Tympanic membrane 



within the skin, around the glands and the hair follicles, some extending on to 

 the upper part of the membrana tympani. The deeper veins of the meatus, 

 which drain the bony and a small part of the cartilaginous meatus, empty into the 

 venous plexus behind the articulation of the lower jaw, those from the upper 

 wall of the meatus extending upward to join the venous plexus which spreads out 

 over the skull. 



The lymphatics of the external auditory canal arise from a cutaneous net-work 

 from which trunks pass in three general groups, as do those of the auricle, (i) 

 The trunks of the posterior group arise in the posterior wall of the external meatus 



and empty, for the most part, into 

 the posterior auricular (mastoid) 

 nodes. Some, however, avoid this 

 first station and join the efferent 

 vessels of the upper nodes of the 

 superior deep cervical chain. (2) 

 The inferior group includes a vari- 

 able number of trunks coming from 

 the lower wall of the external audi- 

 tory meatus, some of which pass to 

 the nodes placed along the course 

 of the external jugular vein at its 

 exit from the parotid, whilst others 

 end in the mastoid nodes. (3) 

 The anterior group is from the 

 concha and the anterior wall of the 

 meatus. These vessels are tribu- 

 tary to the parotid nodes, more 

 particularly to the anterior auricular 

 nodes situated immediately in front 

 of the tragus. 



Nerves. The sensory nerves 



supplied to the external auditory canal are derived from the auriculo-temporal 

 branch of the trigeminus and from the auricular branch of the pneumogastric. The 

 latter, also known as Arnold' s nerve, perforates the wall of the meatus and supplies 

 its lining membrane. 



Practical Considerations : The Auricle. The auditory mechanism may 

 be said to consist of two portions that which conducts the sound and that which 

 receives it. The former is represented by the external and the middle ear ; the 

 latter, by the internal ear. The function of the auricle is to collect and intensify 

 the sound-waves and to direct them into the external auditory canal. That it 

 does not play a very important part in hearing is shown by the fact that its 

 removal has been followed by comparatively little loss in the acuteness of hearing 

 (Treves). Complete absence of the auricle is exceedingly rare ; partial defect 

 i miiiolia ) is more frequent ; while congenital fistulae are comparatively common. 

 These fistula are considered to be due to a defective closure of the first branchial 

 deft. According to His, however, they are due to deficient union of the crus helicis 

 and tin- cms supratragirus. If a fistula closes at its orifices, a retention cyst, 

 sometimes di-rmoid, may result. The ear may be abnormally large (macrotia), or, 

 M a result <>f defective union of the rudimentary tubercles from which the auricle 

 is developed, auricular appendages < polyotia'} may be met with. A supernumerary 

 auricle m. iv \< iv rarely be found on the side of the neck at the orifice of one of 

 the lo\\cr branchial clefts. 



Ouing to the rich blood -supply of the auricle, wounds heal rapidly. When, 

 houever, they occur near the external auditory meatus and are large, cicatricial 

 closure of the canal must be guarded against. 



Frost-bite is frequent because of the exposure to cold and the lack of protec- 

 tion to the Mood vessels from overlying tissues, since little more than skin covers 

 them. An intense reactive congestion follows, and frequently leads' to gangrene. 



Cast of right external auditory canal, seen from be- 

 hind ; natural size. Drawn from cast made by Professor 

 Randall. 





