A REVISED DESCRIPTION

OF THE

Anatomy of the Elephant’s Ear,BY

ALBERT H. BUCK, M, D„

New York,

Clinical Professor of the Diseases of the Ear, College of Physiciansand Surgeons; Consulting Aural Surgeon, New York

Eye and Ear Infirmary.

[Reprinted from the Transactions of the American OtologicalSociety, 1890.1 s

MERCURY PUBLISHING COMPANY, PRINTERS,NEW BEDFORD, MASS.

1890.

A REVISED DESCRIPTION

OF THE

Anatomy of the Elephant’s Ear,BY

ALBERT H. BUCK, M D„

New York,

Clinical Professor of the Diseases of the Ear, College of Physiciansand Surgeons; Consulting Aural Surgeon, New York

Eye and Ear Infirmary.

[Reprinted from the Transactions of the American OtologicalSociety, 1890.]

MERCURY PUBLISHING COMPANY, PRINTERS,NEW BEDFORD, MASS.

1890,

A REVISED DESCRIPTION OF THE ANATOMYOF THE ELEPHANT’S EAR.

Albert H. Buck, M. D., New Toi-k, N. T.

The discovery made by Dr. Richards, that the plane ofsection, which I had taken to be a horizontal plane, wasin reality vertical, renders a large part of the descriptionwhich I published in the Transactions of 1888 inaccurate.The restrictions under which I was placed by Prof. Wilder,who desired to preserve the specimen in as perfect a con-dition as possible for the Cornell Museum of Anatomy,rendered it an easy matter to be misled in regard to tbetrue relations of these different sawed surfaces, to a verticalantero-posteriOr and a vertical transverse plane, and thismust serve as my apology for the error which I was sounfortunate as to make. Thanks to the removal of theserestrictions at a later date by Prof. Wilder, colleaguehas been enabled to study the specimen more thoroughlythan I could, and he has determined accurately the rela-tions of these different parts. With the Society’s permis-sion, therefore, I submit herewith, for publication in thisyear’s volume of the Transactions, a corrected version ofthe account which was printed year before last.

The specimen had been sawed out from the skull insuch a manner as to show four plane and two uneven sur-faces. The plane surfaces are : a vertical one, which issituated just in front of the external auditory canal and mid-dle ear, leaving both of them intact, but traversing many

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of the large air cells which surround these parts; an in-ferior transverse section, which bisects the lower end ofthe middle ear a short distance below the point where itmerges into the Eustachian tube ; a superior horizontal sec-tion which passes through an intercommunicating system ofair cells ; and, finally, a median vertical section which leavesone condyle of the occipital part of the occipito-vertebralarticulation attached to the specimen. The outer and pos-terior face of the specimen represents the natural surfaceof the skull as it appears after the soft parts have been toa great extent removed. The second specimen containsthe entire Eustachian tube of the right side, trom itspharyngeal orifice to its termination in the narrowed lowerend of the middle ear. The third specimen consists of themembranous portion of the 'left Eustachian tube, dividedtransversely at a point about five inches from its pharyngealorifice, and slit up longitudinally throughout a large partof its length. All the specimens are preserved in alcohol.

The external auditory canal.—The auricle had been cutaway as close to the skull as possible, and all that remainsof the cartilaginous portion of the canal is represented bytwo overlapping, funnel-shaped gutters of cartilage, whichtogether form a complete conical framework around theskin-lined orifice of the external auditory canal. This ori-fice, which is nearly circular in shape, measures 9 millime-ters in diameter. It enters the skull in a direction nearlyparallel with the plane of the transverse vertical section.At a distance of about 2 centimeters from the orifice, thecanal begins to bend backward in its course, and at thesame time its calibre becomes considerably larger. At adistance of 7 centimeters from the external orifice it measures15 millimeters in diameter. In the vicinity of the mem-brana tympani the calibre of the canal again diminishes insize, —to 9 or 10 millimeters, as nearly as I could ascer-tain. The ring of cartilage, representing, so to speak, the

ANATOMY OF THE ELEPHANT’S EAR. 5

insertion of the auricle, loses itself in the cutaneous liningof the canal at a distance of about centimeters from theouter orifice. 1 The entire length of the canal from theexternal orifice to the membrana tympani, measures 161-centimeters, or about inches. The skin lining the canal,

Fig. 1. Vertical transverse section of the skull, a little in front of the externalauditory canal. To expose the latter throughout the greater part of its course, theanterior wall of the bony cylinder has been chiseled away. (Reduced to one-third of the natural size of the parts.)

lln this particular specimen the canal was found to be filled through-out its entire length with a semi-solid material which looked like anadmixture of cerumen and cast-off epidermis scales. The natural infer-ence was, that the sedentary life and the unwholesome diet (candies,peanuts, etc.) to which show elephants are almost necessarily subjected,had produced this condition of what, in a human being, would be termedeczema.

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for a distance of about 2 centimeters (| inch) from theorifice, presents a finely corrugated appearance, the foldsrunning in a direction parallel with the long axis of thecanal. From this point inward, as far as to the drum-mem-brane, it presents a smooth, almost polished appearance.

As may be seen in the figure, which represents the partsreduced to one-third of their natural size, the cylinder ofbone constituting the external auditory canal lies in themidst of a labyrinth of intercommunicating cells or cham-bers of varying size and shape. About midway betweenthe drum-membrane and the outer orifice this bony cylinderlies below a cavity of unusual size. How far this cavityextends upward I am unable to determine, as the upperpart of the skull is not before me ; but that part of thecavity which is visible in the specimen measures a littleover 11 centimeters (4| inches) in its transverse, and atleast 15 centimeters (6 inches) in its vertical diameter ; thislatter measurement extending from the surface of the section(superior transverse horizontal section) to the lower limitsof that portion of the cavity which lies below and in frontof the bony cylinder. x\ll these (presumably) air cham-bers communicate freely with each other, sometimes byvery broad openings. So far as lam able to find out bycareful exploration with a probe and by forcing smokethrough different channels, these cavities do not communi-cate with the tympanum proper, but do apparently com-municate directly with the nasal system of cavities. Inthe human being the pneumatic cells do not communicatewith the cavities belonging to the nasal system exceptthrough the Eustachian tube. In this respect, therefore,the mastoid cells' of the elephant differ materially fromthose of man.

l ln the human being pneumatic cells are found not only in the mastoidprocess, but also above the dense cylinder of bone which immediately sur-rounds the calibre of the external auditorj' canal,—that is, in the very samelocality as that occupied by the cells here under consideration. Hyrtl, in

ANATOMY OK THE ELEPHANT’S EAR. 7

v The Eustachian tube, from its pharyngeal 1 or nasal ori-fice to the point where it emerges into the tympanic sys-tem of cavities, measures 11 centimeters (4| inches). Itsnasal orifice, in the present specimen, is more or less muti-lated ; but it is evident that in its general features and sizeit resembles very closely the pharyngeal end of the humanEustachian tube. The latter is perhaps a trifle larger, andit stands out more prominently from the surrounding surfaceof the mucous membrane. Toward the tympanum thetube ends in a nicely rounded orifice, one side of whichapparently corresponds with the termination of the longand thick cartilaginous cylinder, around which the tube iscurved, gutter-like. As the specimen had been preservedin alcohol for two or three months I was not able to makeout satisfactorily, by simple naked-eye inspection, the exactrelations of the different tissues of the tube to each other.At the two orifices the calibre appeared to be small, i. e.,simply large enough to admit easily a large-sized probe.A section near the middle portion of the tube revealed atfirst no calibre whatever, the opposite walls being appar-ently in perfect contact at all points. By manipulatingthe specimen, however, these closely applied walls couldbe made to separate, thus revealing to view a calibre largeenough to admit the little and perhaps even the third finger.The top part of a question mark represents fairly well thecr<sss section of the calibre of the tube, when in a state ofrest, at a point about half-way between the two orifices.Toward the tympanum the tube does not open directly into

his “Anatomische Untersuchungen liber das Gehororgan des Menschenund der Saugethiere” (Prag, 1845), sa Js that “the pars mastoidea of thetemporal bone is, according to Kostlin, wanting in the hippopotamus, theelephant, and the rhinoceros.”

xThe specimen is too fragmentary in character to warrant me in drawingany conclusion whatever in regard to the relations of the peripheral endof the Eustachian tube to the nasal and pharyngeal cavities. It is for thisreason that I employ the terms pharyngeal and nasal indifferently.

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the tympanic cavity proper, but into an elongated air cham-ber, which lies anteriorly to this cavity, and opens into itthrough an elongated slit-shaped opening. This chambercommences as a cul-de-sac at the orifice of the tube, andgradually increases in size, throughout a length of between4 and 5 centimeters (about 2 inches). Like all the airchambers thus far mentioned, its walls consist of thin bonelined with a smooth mucous membrane. The antero-posterior diameter of the cavity, at a distance of centi-meters from the orifice of the tube, measures nearly threecentimeters inches) ; the breadth varies but does not ex-ceed 1|- centimeters (| inch) at any part. The openingfrom this chamber into the tympanum proper is an elonga-ted slit and presents one or two peculiarities. The edgeof the opening, on the side toward the median line, is pro-vided with two odd-looking osteophytes, one resemblinga cock’s comb, the other a padded drum-stick, such as isused in beating a big bass drum. The slender handleof this miniature drum-stick is perhaps 4 millimeters longand scarcely half a millimeter thick, and at the end of itis a well rounded knob, fully two millimeters in length andabout a millimeter and a half in thickness. 1

yrtl says nothing about the occurrence of these osteophytes in theelephant in particular, but he refers to their existence in some animals inthe following words: “In certain animals possessing a roomy tympaniccavity there are found, either in the middle ear proper or in some of thecavities which communicate with it, bony outgrowths of characteristicshape. As these objects are found, with rare exceptions, to be always ofabout the same size and to occupy relatively the same positions, the infer-ence is permissible that they are notmere accidental formations, but prob-ably possess some functional importance. ******* In theposterior segment of the bulla [tympanica] of the lion these curiousstructures attain their highest degree of development, and may be seenhere in the form of pear and othei' shaped bodies springing by a slender(sometimes hairlike) stem from the floor of this cavity.” From thisdescription, and also from the pictorial representations which he gives ofthese bodies, it is clear that they are identical with those which I havedescribed above.

ANATOMY OF THE ELEPHANT’S EAR. 9

Still another peculiarity is observable at the openingwhich leads from the Eustachian vestibule, if I may so callit, into the tympanum proper. A little behind the openingthe back wall of the vestibule becomes sharply groovedvery much like the groove of bone which, in the humanbeing, holds the belly of the tensor tympani muscle andruns upward, and finally a little forward to the anterior andmiddle portion of what may properly be termed the annulus

Fig. 2. View of themembrana tympani and grooved ante-ro-external wall of the passage leading from the tym-panum proper to the Eustachian tube. The sharp-edgedridge running along the middle of the grooved antero-external wall and dividing it into two subordinateshallowgrooves, may be seen in the picture. (Aboutone-third natural size.)

tympanicus. This groove extends so far outward that itsouter wall is well outside of the plane of the drum-mem-brane. The anterior wall of the vestibule constitutingone of the two grooves already mentioned displays threeopenings two oval in shape and one nearly circularwhich lead into adjacent air chambers ; the other grooveis smooth and free from openings throughout its entirelength. The chambers just mentioned have no communi-cation one with another, nor with any of the neighboringcavities. The antero-posterior diameter of the vestibule is21 millimeters (nearly | inch). The breadth of the pos-terior wall, opposite the osteophytes, is 1 centimeter (|

inch).The tym-panic cavity. — Looked at from below, this

cavity seems to be separated into two parts by a pro-jecting mass of bone, the sides of which form, roughly, anangle of 45°. That part of the cavity which lies nearerthe median line is considerably larger than that which isin the immediate neighborhood of the drum-membrane.The roof of this outer cavity (or tympanum proper) pos-

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sesses certain peculiarities which will be described morefully by Dr. Richards.

The antero-posterior diameter of the tympanic cavity,directly abreast of the membrana tympani, is 27 millime-ters inches) and its average breadth 25 millimeters(about 1 inch). Its height could not be accurately ascer-tained, but it must have been at least 50 millimeters (2inches).

The outer wall is made up of the grooved structureswhich I have described above, and of the memhrana tym-

■pani. This latter membrane, which is shown fairly wellin Figs. 2 and 4, is decidedly conical in shape, as seen from

Fig. 3. View of thetympanic cavity from within, showing (distinctly in the photo-graph but very faintlyin the engraving) the stall-like openings behind and belowthe door of the tympanum, a part of the jagged wall surrounding the mouthof the well-like excavation, the two osteophytes and the grooved outer wall ofthe passageway leading from the tympanum to the Eustachian tube. (Slightlyreduced in size.) 1

the side of the tympanum, while the surface of the mem-brane on the side toward the external auditory canal pre-sents scarcely any hollowing-out at all,—barely enough to

l The difficulties encountered in photographing the middle ear fromdifferent points of view were found to be very great, and as a consequencethe half-tone pictures which accompany this article leave very much to bedesired in the way of clear definition.

ANATOMY OF THE ELEPHANT’S EAR. 11

justify the use of the expression, a shallow cone. Thislack of agreement between the two surfaces is due appar-ently to two facts : the marked curving inward of the tipend of the manubrium mallei, and the great thickness ofthe soft parts in the vicinity of the umbo of the membrane.From the great resistance which the latter offers to pressuremade at any point of its surface I should infer that itsthickness is at no point less than one millimeter. As awhole the membrane is nearly circular in shape and meas-ures fully two centimeters (| inch) in diameter.

Superiorly the tympanic cavity terminates in a cul-de-saccomposed of soft tissues, which form a thick diaphragmseparating the tympanum proper from a second, muchsmaller cavity containing the head of the hammer, all ofthe anvil, and presumably the stirrup. From the posteriorpart of this cul-de-sac the chorda tympani nerve passes for-ward, and then outward, in the form of a strong roundedcord, across the inner aspect of the neck of the hammer,at right angles to the manubrium. There is apparently notrace whatever of a tensor tympani muscle.

The comparatively small area of bone surface constitutingthe inner wall of the tympanic cavity proper presents, di-rectly opposite the umbo of the drum-membrane, a roundedeminence in which no openings are visible. This is proba-bly the analogue of the promontory in the human being.Behind it, and situated at a higher level, is a rounded ridgeof bone which terminates in a hooded opening or niche,suggesting the niche for the fenestra rotunda ; but a carefulexploration with the probe fails to detect any break in thehard, bony surface at the bottom of the niche. 1 Further-

I Hjrtl (op. cit.) says that the fenestra rotunda, in the elephant, is to befound behind an angular overhanging projection of the promontory, andthat the actual opening of communication between the tympanum andthe scala tympani is a mere narrow slit. He quotes Cuvier as saying thatthe fenestra rotunda of the elephant is very small, irregular in shape, andconcealed behind a projecting part of the promontory. At the same time

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more, this niche faces forward and inward, whereas thatof the fenestra rotunda in the human being faces backwardcD

and outward, and its position is altogether too far removedfrom the stirrup. The mere use of a probe is not sufficientto determine this question satisfactorily and I must, there-fore, leave it unsettled. The rest of the inner wall of thetympanum, down to the point where it bends abruptlyaround the blunt anterior edge of the promontory describedabove, presents no features of special interest.

The posterior wall of the tympanum, in the vicinity ofthe promontory, is smooth, but on a line with the posteriormargin of the annulus tympanicus it terminates abruptlyin a thick, rounded edge which projects free into the airspace. This edge represents the inner and lower termina-tion of the bony cylinder constituting the external auditorycanal. In the excavation behind and beneath the edgeof bone just mentioned may be seen three sharp-edgedmembranous septa, dividing the space into three deeply-shaded. r.ecesses and one shallow cul-de-sac, all facingobliquely inward. Taking them in regular order fromabove downward I explored each stall with the probe, andfound that the first one is a mere cul-de-sac, extending toonly a slight depth. The second one, which presents thelargest opening, measures 33 millimeters (1| inches) inlength and runs apparently directly behind, and nearly inthe same direction with, the external auditory canal. Bywithdrawing the probe a short distance and at the sametime causing it to press against the antero-inferior wall ofthe channel, one becomes conscious that the end of theinstrument reaches the free edge of an elastic septum thatdivides this second stall into two subordinate channels. Thelong axis of this second subordinate channel measures 30millimeters (1| inches). The third stall is somewhat nar-

he states that Kick (Ue.ber das Labyrinth des Elephanten, in Mueller’sArchiv, 1844, p. 431) believes that this opening' is the outlet of the aquae-ductus cochleae, and that the elephant has no true fenestra rotunda.

ANATOMY OF THE ELEPHANT’S EAR. 13

rower at the entrance than the one just described. Itconsists apparently of a single passage without any bifur-cations, and measures, from the entrance to its farther end,nearly 70 millimeters (3| inches). Its general directioncorresponds quite accurately with that of the external audi-tory canal. The fourth stall has a length of 53 millimeters(3 inches), and its long axis, whose general direction isoutward, forms an angle of about 40° with the axis of theexternal auditory canal. The floor is lacking close to theentrance, and the space is occupied by a deep excavationfrom which the probe passes downward into a large cham-ber.

The pit into which the stalls open is characterized bythe presence, on its inner side, of a honey-comb structurewhich projects to such a degree as to partially conceal theentrances to the stalls. One of them is particularly con-spicuous by reason of its perfectly cylindrical shape, by thejagged character of its free edge, and by the depth (30millimeters—| inch) of the enclosed well, which seems tohave no communication with any of the adjacent cavities.

The large cavity which I mentioned in the earlier partof this description as forming an acute angle with thetympanum proper, presents few features of special interest.Its total length, or rather height, is approximately 50 milli-meters (3 inches) ; its maximum transverse diameter is 30millimeters inches) and the minimum 30 millimeters ( |

inch). At the upper and back part of this subsidiary tym-panic cavity are two triangular openings with smoothlyrounded edges. The inferior opening seems to lead intothe general system of air cells which surround the exter-nal auditory canal; the superior opening leads into a longcavity, or system of cavities, which certainly do not com-municate with these cells. A probe introduced into thissuperior opening can be passed, in an outward and some-what upward direction, to a distance of 85 millimeters

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(3-| inches) without encountering any resistance. Severalother openings are visible along the outer wall of the sub-sidiary tympanic cavity, but with one exception they alllead into shallow pockets or diverticula. In this singleexceptional instance a slightly curved probe can be passedin to a depth of 25 millimeters (1 inch). This small curv-ing cavity is situated in the mass of bone which forms the

Fig. 4. View of the subsidiary tympanic cavity as seen from within and behind,after the removal of the greaterpart of the anterior and upper boundaries. (Nat-ural size.)

angle between the tympanum proper and the larger sub-sidiary cavity.

We come, finally, to the consideration of the small cavitylying above and behind the tympanum proper, the cavitycontaining the anvil, the body or head of the hammer, andpresumably the stirrup. The plate of bone covering boththis cavity and that of the tympanum proper was found to

ANATOMY OF THE ELEPHANT’S EAR. 15

be of considerable thickness, probably at least 5 millime-ters ( T

3g inch) thick. This smaller cavity, as we havementioned before, is entirely shut off from the tympanumproper. It is, roughly measured, about ten millimetersinch) square. From the forward and outer corner of thiscavity a probe can be passed, in a direction parallel withthe long axis of the external auditory canal, a distanceof 55 millimeters (2| inches) before it encounters anyobstacle. By the smoke test it appears that this cavity orchannel is a closed sac, having no communication with theadjacent system of pneumatic cells, and therefore not rep-resenting, in a physiological sense, the analogue of themastoid antrum in the human being.

The space between the tegmen tympani and the head ofthe hammer and body of the anvil, was found to be filledwith a mass of soft connective tissue (almost like adiposetissue). Its removal disclosed to view the interlockingmalleo-incudal joint. The body of the anvil overtowersthe head of the hammer; that is, it is decidedl}’ nearerthe tegmen tympani. There is quite free play betweenthe two ossicles, both of which, however, may be de-scribed as being very solidly anchored in their respectivepositions. Considerable force may be applied to the handleof the hammer near the the membrana tympanibefore any visible excursion of the head of this ossicle canbe distinguished. The same degree of force applied to thehandle of the hammer apparently fails to produce anymotion whatever in the anvil. Direct pressure upon thelatter must be of a very decided character before visiblemotion can be excited in it. A strong membranous cap-sule spans the space between the opposite edges of themalleo-incudal joint.