112 6 THE ORGANS OF SPECIAL SENSE 



should be borne in mind in introducing the aural speculum, so that it shall not be 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 osseous 

 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 the membrana 

 tympani. Just in front of the 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 become 

 lodged. By aid of the speculum, combined with traction of the auricle upward and backward, 

 the whole of the membrana tympani is rendered visible. It is a pearly-gray membrane, slightly 

 glistening in the adult, placed obliquely, so as to form with the floor of the meatus a very acute 

 angle (about 55 degrees), while with the roof it forms an obtuse angle. At birth it is more hori- 

 zontal being situated in almost the 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 (Fig. 837). At the upper part of this streak, close to the roof of the meatus, a little 

 white rounded prominence is plainly to be seen; this is the processus brevis of the malleus, 

 projecting against the membrane. The membrana tympani does not present a plane surface; 

 on the contrary, its centre is drawn inward, on account of its connection with the handle of the 

 malleus, and thus the external surface is rendered concave. 



The connections of the nerves of the auditory canal explain the fact of the occurrence, in cases 

 of any irritation of the meatus, of constant coughing and sneezing from implication of the 

 vagus, or of yawning from implication of the auriculotemporal, of vomiting which mav follow _ 

 syringing the ears of children, and the occasional hearf failure similarly induced in elderly per- 

 sons. No doubt also the association of earache with toothache in cancer of the tongue is due 

 to implication of the inferior maxillary, which supplies also the teeth and the tongue. The 

 upper half of the membrana tympani is much more richly supplied with blood than the lower 

 half. For this reason, and also to avoid the chorda tympani nerve and ossicles, incisions through 

 the membrane should be made at the lower and posterior part. 



Applied Anatomy. -Malformations, such as imperfect development of the external parts, 

 absence of the meatus, or supernumerary auricles, are occasionally met with. Or the pinna may 

 present a congenital fistula, which is due to defective closure of the first visceral cleft, or rather 

 of that portion of it which is not concerned in the formation of the Eustachian tube, tympanum, 

 and meatus. In some cases the cephaloauricular angle is almost absent; in others, it is nearly 

 a right angle. Projecting ears and long ears are said by some observers to be more common 

 among degenerates, criminals, and the insane than among the normal, the non-criminal, and 

 the sane. The skin of the auricle is thin and richly supplied with blood, biAin spite of this it 

 is frequently the seat of frost-bitffjdtife to the fact that it is much exposed to^cjld, and lacks the 

 usual underlying subcutaneous fat found in most other parts of the body. < A collection of blood 

 is sometimes found between the cartilage and perichondrium (hematoma auris), usually the 

 result of traumatism, but not necessarily due to this cause. It is said to occur most frequently 

 in the ears of the insane. Keloid sometimes grows in the auricle around the puncture made for 

 ear-rings, and epithelioma occasionally affects this part. Deposits of urate of soda are often met 

 with in the pinna in gouty subjects. 



The external auditory meatus can be most satisfactorily examined by light reflected down a 

 funnel-shaped speculum; by gently moving the latter in different directions and by gently 

 drawing the pinna upward, backward, and a little outward, so as to render the canal as straight 

 as possible, the whole of the canal and membrana tympani can be brought into view. The 

 points to be noted are the presence of wax or foreign bodies, the size of the canal, and the con- 

 dition of the membrana tympani. The accumulation of wax (impacted cerumen) is often the 

 cause of deafness, and may give rise to very serious consequences, causing ulceration of the 

 membrane and even absorption of the bony wall of the canal. Foreign bodies are not infrequently 

 introduced into the ear by children, and, when situated in the first portion of the canal, may be 

 removed with tolerable facility by means of a minute hook or loop of fine wire, the parts being 

 illuminated with reflected light; but when they have slipped beyond the narrow middle part of 

 the meatus, their removal is in nowise easy, and attempts to effect it, in inexperienced hands, 

 may be followed by destruction of the membrana tympani and possibly injury of the contents of 

 the tympanum. The caliber of the external auditory canal may be narrowed by inflammation 

 of its lining membrane, running on to suppuration; by periostitis; by polypi, sebaceous tumors, 

 and exostoscs. 



THE MIDDLE EAR, DRUM, OR TYMPANUM (AURIS MEDIA) 



(Figs. 835, 839). 



The middle ear or tympanum is an irregular cavity, compressed laterally, 

 and situated within the petrous portion of the temporal bone. It is placed above 



