THE EAR. 915 



ami osseous portion of the tube, and covers the surface of the membrana tympani, 

 forming its outer layer. After maceration the thin pouch of epidermis, when 

 withdrawn, preserves the form of the meatus. In the thick subcutaneous tissue 

 of the cartilaginous part of the meatus are numerous ceruminous glands, which 



Cartilage of 

 the piniut ' 



Promonl. 



Cartilage of the act. 

 auditory meatus 



FIG. 511. Transverse section of external auditory meatus and tympanum. Left side. (Gegenbaur.) 



secrete the ear-wax. They resemble in structure sweat-glands, and their ducts 

 open on the surface of the skin. 



The a rtf i-(>'* supplying the meatus are branches from the posterior auricular, 

 internal maxillary, and temporal. 



The a >'/>.<'* are chiefly derived from the auriculo-temporal branch of the inferior 

 maxillary nerve. 



Surface Form. At the point of junction of the osseous and cartilaginous portions the tube 

 forms an obtuse angle, which projects into the tube at its antero-inferior wall. This produces a 

 sort of constriction in this situation, and renders it the narrowest portion of the canal an im- 

 portant point to be borne in mind in connection with the presence of foreign bodies in the ears. 

 The cartilaginous is connected to the bony part by fibrous tissue, which renders the outer part 

 of the tube very movable, and therefore by drawing the pinna upward and backward the canal 

 is rendered almost straight. At the external orifice are a few short, crisp hairs which serve to 

 prevent the entrance of small particles of dust, or flies or other insects. In the external auditory 

 meatus the secretion of the ceruminous glands serves to catch any small particles which may 

 find their way into the canal, and prevent their reaching the membrana tympani, where their 

 I'lVM/nce mi-rht excite irritation. In young children the meatus is very short, the osseous part 

 being very deficient, and consisting merely of a bony ring (the tympanic plate), which supports 

 the membrana tympani. In the foetus the osseous part is entirely absent. The shortness of the 

 canal in children should be borne in mind in introducing the aural speculum, so that it be not 

 pushed in too far. at the risk of injuring the membrana tympani ; indeed, even in the adult the 

 speculum should never be introduced beyond the constriction which marks the junction of the 



is and cartilaginous portions. In using this instrument it is advisable that the pinna 

 should be drawn upward, backward, and a little outward, so as to render the canal as straight as 

 possible, and thus assist the operator in obtaining, by the aid of reflected light, a good view of 

 tiie mernbrana tympani. Just in front of tbe membrane is a well-marked depression, situated 

 on the floor of the canal and bounded by a somewhat prominent ridge ; in this foreign bodies 

 may ber-.mie lodged. By aid of tbe speculum, combined with traction of the auricle upward and 

 backward, the whole of the membrana tympani is rendered visible. It is a pearly-gray mem- 

 brane, slightly "listening in the adult, placed obliquely, so as to form with the floor of the meatus 

 a very acute angle, while with the roof it forms an obtuse angle. At birth it is more horizontal, 

 situated in almost tbe same plane as the base of the skull. About midway between the anterior 

 and posterior margins of the membrane, and extending from the centre obliquely upward, is a 

 reddish-yellow streak : this is the handle of the malleus, which is inserted into the membrane. 

 At the upper part of this streak, close to the roof of the meatus. a little white rounded promi- 

 nence is plainly to be seen : this is the processus brevis of the malleus, projecting against the 

 membrane. The roembrana tympani does not present a plane surface ; on the contrary, its centre 



twn inward, on account ol its connecnoii Vuii the handle of the malleus, and thus the 

 external surface is rendered concave. 



