THE EAR. 87 



The meatus is supplied by the aiiriculotemporal branch of the fifth and the 

 auricular branch of the pneumogastric nerve. Irritation of the latter nerve is said 

 to be the cause of feeling it in the throat when anything is put in the ear. 



Membrana Tympani. The membrana tympani is inclined downward and 

 inward at an angle of about 140 to the upper wall (Troltsch) and 27 to the lower 

 wall (Bezold) of the meatus ; it does not lie directly transverse, therefore in intro- 

 ducing instruments into the ear the upper posterior part will be first encountered. 

 The membrane is located 2.5 cm. (i in.) from the surface; this is to be borne in 

 mind in puncturing the membrane or other operations. The membrane has three 

 coats: an outer, continuous with the skin of the meatus; a fibrous or middle layer; 

 and an internal or mucous layer, continuous with the lining of the tympanic cavity. 

 The membrana tympani at birth is fastened at its circumference to the tympanic 

 bone, which unites with the other portions of the temporal bone soon after birth. 

 This ring of bone is incomplete at its upper portion for a distance equaling one-eighth 

 of its circumference. This is called the notch of Rivinus. The fibrous layer does 

 not extend across this notch, which is closed by the mucous membrane on the inside 

 and by the skin layer of the membrane on its outer side. The part closing the notch 



/Membrana flaccida 



Short process of malleus 



Long handle of malleus - 



Cone of light 

 FIG. 102. Outer surface of the tympanic membrane of the left ear. 



is called ShrapnelV s membrane or membrana flaccida. As it possesses no fibrous 

 layer it is weaker than the membrane elsewhere and consequently is a favorite spot 

 for pus to perforate in order to find exit from the middle ear. 



In examining the membrane by means of light thrown into the meatus through 

 a speculum by the head mirror, one sees extending downward from its centre a small 

 cone of light; any depression or bulging 'of the membrane will cause this cone of 

 light to be altered in its position, or even cause it to disappear entirely. From the 

 centre of the membrane upward extends a line which indicates the attachment of the 

 long handle of the malleus, one of the bones of the middle ear. Stretching across 

 the upper portion is the membrane of Shrapnell or membrana flaccida, so called on 

 account of its not being so tense as the remaining portion. It is better supplied 

 with blood-vessels than the other portion. 



The membrana tympani is of surgical interest on account of its being often dis- 

 tended or perforated. A purulent discharge from the ear usually indicates disease 

 of the middle ear or tympanum. If pus is coming from a furuncle of the meatus, the 

 latter will be swollen and its source can readily be recognized. If it comes from 

 outside of the meatus, as in cases of suppuration of the parotid gland, it will be recog- 

 nized by an examination of the gland. There is no other source of pus but the 

 middle ear and for it to gain exit it must perforate the membrane; this perforation 

 can usually be seen with the speculum and head mirror, as can also bulging. 



In inflammation of the middle ear the effused serum or pus bulges the mem- 

 brane outward. When this condition is accompanied, as it often is, by intense pain, 



