A CONTRIBUTION TO THE

ANATOMY OF THE ELEPHANT’S EARBY

ALBERT H. BUCK, M. D.,

Clinical Professor of the Diseases of the Ear, College of Physicians and Surgeons,New York.

[Ke-printed from The Transactions of the American Otologica e Society, 188S.]

MERCURY PUBLISHING COMPANYPRINTERS

NEW BEDFORD, MASS

A CONTRIBUTION TO THE ANATOMY OF THEELEPHANT’S EAR.

Albert H. Buck, M. D., New Torlc,N. 7

The specimens which I am about to describe were verykindly sent to me for dissection by Prof. Burt G. Wilder,M. D., of Cornell University. The largest of the threerepresents the greater part of the right temporal bone of thelarge show elephant, Alice, the mate of the famous Jum-bo. It had been sawed out from the skull in such a man-ner as to show four plane and two uneven surfaces. Theplane surfaces are : a horizontal one, which is situated justabove the level of the external auditory canal and middleear, leaving both of them intact, but traversing many ofthe large air cells which surround these parts ; an anteriortransverse vertical section, which bisects the anterior endof the middle ear a short distance back of the point whereit merges into the Eustachian tube : a posterior transversevertical section which passes through a communicating sys-tem of air cells and, finally, a median antero-posteriorvertical section which leaves one condyle of the occipitalpart of the occipito-vertebral articulation attached to thespecimen. The outer and the lower faces of the specimenrepresent the natural surfaces of the skull as they appearafter the soft parts have been entirely removed. The sec-ond specimen contains the entire Eustachian tube of theright side, from its pharyngeal orifice to its termination inthe narrowed anterior end of the middle ear. The thirdspecimen consists of the membranous portion of the left

JThe planes of these two sections form a sharply acute angle with eachother, as will be seen by an examination of Fig. i.

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Eustachian tube, divided transversely at a point about fiveinches from its pharyngeal orifice, and slit up longitudinallythroughout a large part of its length. All the specimensare 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 horizontal section. At a dis-tance of about 2 centimeters from the orifice, the canalbegins to bend downward in its course, and at the same

Fig. 1. Horizontal section of tlie skull, a little above the level of the external audi-tory canal. To expose the latter throughout the greater part of its course, theupper wall of the bony cylinder has been chiseled away. (Reduced to one-thirdof the natural size of the parts.)

time its calibre becomes considerably larger. At a dis-tance of 7 centimeters from the external orifice it measures

ANATOMY OF THE ELEPHANT’S EAR. 5

15 millimeters in diameter. In the vicinity of the mem-brana tympani the calibre of the canal again diminishes insize—to 9or 10 millimeters, as nearly as I could ascer-tain. The ring of cartilage, representing, so to speak, theinsertion 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, measurescentimeters, or about 6\ inches. The skin lining the canal,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 containing the external auditory canal lies in themidst of a labyrinth of inter-communicating cells or cham-bers of varying size and shape. About midway betweenthe drum-mernbrane and the outer orifice this bony cylinderlies in front of a cavity of unusual size How far thiscavity extends posteriorly I am unable to determine, as theback part of the skull is not before me ; but that part of thecavity which is visible in the specimen measures a littleover it centimeters inches) in its transverse, and atleast 15 centimeters (6 inches) in its antero-posterior diam-eter ; this latter measurement extending from the surfaceof the section (posterior transverse vertical section) to theanterior limits of that portion of the cavity which lies in

l ln 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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frontofand above the bony cylinder. All these (presumably)air chambers communicate freely with each other, some-times by very broad openings. So far as lam able to findout by careful exploration with a probe and by forcingsmoke through different channels, these cavities do not com-municate with the tympanum proper, but, as will be seenfarther on, they do communicate atone point with what Ihave termed the subsidiary tympanic cavity. On the otherhand, they apparently communicate directly with thenasal system of cavities. In the human being the mastoidcells do not communicate with the cavities belonging to thenasal system except through the Eustachian tube. In thisrespect, therefore, the mastoid cells' of the elephant differmaterially from those of man.

The Eustachian tube, from its pharyngeal 2 or nasal ori-fice to the point where it emerges into the tympanic sys-tem of cavities, measures u centimeters 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 surface

x 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 auditory canal,—that is, in the very same

locality as that occupied by the cells here under consideration. Hyrtl, inhis “Anatomische Untersuchungen liber das Gehororgan des Menschenund der Saugethiere” (Prag, 1845), says that “the pars mastoidea of thetemporal bone is, according to Kostlin, wanting in the hippopotamus, theelephant, and the rhinoceros.” But this statement probably has referencemerely to the absence of a visible bony prominence behind and below theorifice of the external auditory canal, and is not to be interpreted as signi-fying that these three animals lack the system of communicating pneu-matic cells which constitutes the essential feature of the mastoid process.

2 The 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.

ANATOMY OF THE ELEPHANTS EAR. 7

of the mucous membrane. Toward the tympanum thetube ends in a nicely rounded orifice, one side of whichapparently corresponds with the termination of the long andthick 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 thecross 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 intothe tympanic cavity proper, but into an elongated air cham-ber, which lies at a somewhat higher level than this cavity,and opens into it through an elongated slit-shaped opening.This chamber commences as a cul-de-sac at the orifice ofthe tube, and gradually increases in height and slightly inbreadth, throughout a length of between 4 and 5 centime-ters (about 2 inches). Like all the air chambers thus farmentioned, its walls consist of thin bone lined with a smoothmucous membrane. The height of the cavity, at a dis-tance of 3|- centimeters from the orifice of the tube, meas-ures nearly three centimeters inch); the breadthvaries but does not exceed centimeter (-| inch) at anypart. The opening from this chamber into the tympanumproper is an elongated slit and presents one or two pecu-liarities. The edge of the opening, on the side toward the

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median line (V. e., toward the promontory), is provided withtwo odd-looking osteophytes, one resembling a cock’s comb,the other a padded drum-stick, such as is used in beating abig bass drum. The slender handle of this miniature drum-stick is perhaps 4 millimeters long and scarcely half amillimeter thick, and at the end of it is a well roundedknob, fully two millimeters in length and about a milli-meter and a half in thickness. 1

Fig. 3. View of the membrana tympani and arched roofof the passage leading from the tympanum proper tothe Eustachian tube. The sharp-edged ridge runningalong the middle of the ai’ched roof and dividing it intotwo subordinate shallow inverted grooves or arches,may be seen in the picture. (About one-third naturalsize.)

Still another peculiarity is observable at the openingwhich leads from the Eustachian vestibule, if I may so callit, into the tympanum proper. A little below the openingthe floor of the vestibule becomes sharply grooved verymuch like the groove of bone which, in the human being,holds the belly of the tensor tympani muscle and runsslightly upward, backward, and inward to the anterior and

Tlyrtl 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 not mere 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 other-shaped bodies springing by a slender(sometimes hair-like) 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

upper portion of what should probably be termed theannulus tympanicus. As the groove emerges from theopening it becomes a sharply projecting gutter (like thoseplaced under the eaves of houses), and continues as suchclose up to the top of the membrana tympani. (See Fig.2.) The roof of the cavity immediately above this gutter,and running parallel with it, is arched, like a secondinverted gutter. A low but sharply definedridge runs alongthe middle of the arch, dividing it into two minor groovesor arches. The outer one of these two grooves that is,the one lying farthest from the free cavity of the tympanumproper—is smooth and free from openings throughout itsentire length, while the inner one displays three openings

two oval in shape and one nearly circular—which leadinto adjacent air chambers. These chambers have no com-munication one with another, nor with any of the neigh-boring cavities. The height of the space between thegrooved incline and the arched roof is 21 millimeters (nearly| inch). The breadth of the grooved floor, opposite theosteophytes, is 1 centimeter (| inch).

The tympanic cavity -pro-per. —Looked at from in front,the posterior end of this cavity is shaped very much likethat of the human being; all the dimensions being, ofcourse, very much larger. From its anterior portion therebranches off, in a posterior direction, a much larger cavity,the long axis of which forms with the long axis of thetympanic cavity a slightly acute angle. The junction ofthese two cavities converts the promontory into a boldprojecting angle of bone.

The roof common to both these cavities presents no fea-tures of special interest.

The height of the tympanic cavity, directly abreast ofthe membrana tympani, is 27 millimeters (i-Jg- inch) andits average breadth, 25 millimeters (about 1 inch). Itslength could not be accurately ascertained, but it musthave been at least 50 millimeters (2 inches).

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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. 3,3. View of the tympanic cavity from above and in front, showing (distinctly inthe photograph but very faintly in the engraving) the stall-like openings under thefloor of the tympanum, a part of the jagged wall surrounding the mouth of thewell-like excavation, the two osteophytes and the grooved floor of the passage-way leading from the tympanum to the Eustachian tube. (Slightly reduced insize.)*

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 tojustify 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 pres-sure made at any point of its surface I should infer thatits thickness is at no point less than one millimeter. As a

*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.

whole the membrane is nearly circular in shape andmeasures fully two centimeters (| inch) in diameter.

Posteriorly the tympanic cavity terminates in a cul-de-saccomposed of soft tissues, which form a thick diaphragm sep-arating the tympanum proper from a second, much smallercavity containing the head of the hammer, all of the anvil,and presumably the stirrup. From the lower part of thiscul-de-sac the chorda tympani nerve passes outward andforward, in the form of a strong rounded cord, across theinner aspect of the neck of the hammer, at right angles tothe manubrium. There is apparent!} 7 no trace whatever ofa tensor tympani muscle.

The comparatively small area of bone surface constitut-ing the inner wall of the tympanic cavity, presents, directlyopposite 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.Below it, and situated more posteriorly, is a rounded ridge ofbone which terminates in a hooded opening or niche, sug-gesting 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-more, this niche faces forward and inward, whereas thatof the fenestra rotunda in the human being faces back-ward and outward.

The mere use of a probe is not sufficient to determinethis question satisfactorily, and I must, therefore, leave itunsettled. The rest of the inner wall of the tympanum, up

I Hyrtl (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 timehe states that Fick (Ueber das Labyrinth des Elephanten, in Mueller’sArchiv, 1844, p. 431) believes that this opening is the outlet of the aquse-ductus cochleae, and that the elephant has no true fenestra rotunda.

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to the point where it bends abruptly around the blunt ante-rior edge of the promontory just described, presents nofeatures of special interest.

The floor of the tympanum, in the vicinity of the prom-ontory, is smooth, but on a line with the anterior edge ofthe annulus tympanicus, it terminates abruptly in a thick,rounded edge which projects free into the air space. Onemight compare it to the edge of a semi-circular platformsurrounding a deep pit. In this pit, directly under theplatform, may be seen three sharp-edged vertical mem-branous septa, dividing the space into three deeply-shad-owed recesses and one shallow cul-de-sac , all facingobliquely inward and forward. Taking them in regularorder from behind forward I explored each stall with theprobe, and found that the first one is a mere cul-de-sac,extending to only a slight depth beneath the floor of thetympanum. The second one, which presents the largestopening, has no visible floor, but the latter is found, onexploration with the probe, to lie at some distance belowthe lower edge of the entrance. The long axis of this stallmeasures 33 millimeters (i|- inch) and it runs apparentlydirectly underneath, and nearly in the same direction with,the external auditory canal. By withdrawing the probe ashort distance and at the same time causing it to pressagainst the anterior wall of the channel, one becomes con-scious that the end of the instrument reaches the free edgeof an elastic septum that divides this second stall into twosubordinate channels. The long axis of this second sub-ordinate channel measures 30 millimeters (ifa inch). Thethird stall is somewhat narrower at the entrance than theone just described. It consists apparently of a single pas-sage without an}' bifurcations, and measures, from the en-trance to its farther end, nearly 70 millimeters (2| inches).Its general direction corresponds quite accurately with thatof the external auditory canal. The fourth stall has a

ANATOMY OF THE ELEPHANT’S EAR. 13

length of 52 millimeters (2 inches), and its long axis, whosegeneral direction is outward, forms an angle of about 40°with the axis of the external auditory canal. The floor islacking close to the entrance, and the space is occupied bya deep excavation from which the probe passes outwardand forward into a large chamber that apparently belongsto the system of nasal or frontal cells.

The pit lying in front of the stalls which I have justdescribed, has a honeycombed floor ; the comb-like struc-tures rising up to such a height 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 upper edge, and by the depth(20 millimeters—| inch) of the enclosed well, which seemsto have no communication with any of the adjacent cavi-ties.

The large cavity which I mentioned in the earlier part ofthis description as forming a slightly acute angle with thetympanum proper, presents few features of special inter-est. Its total length is approximately 50 millimeters (2

Fig. 4. View of the subsidiary tympanic cavity from in front, after the removalof the greater part of the anterior and upper boundaries. (Natural size.)

inches) ; its maximum transverse diameter is 30 millimeters

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inch) and the minimum 20 millimeters (| inch). Atthe lowest point of this subsidiary tympanic cavity are twotriangular openings with smoothly rounded edges. Theanterior opening leads into the general system of air cellswhich surround the external auditory canal ; the posterioropening leads into a long cavity or system of cavities which(as shown by the smoke test) do not communicate withthese cells. A probe introduced into this posterior openingcan be passed, in an outward and somewhat upward di-rection, to a distance of 85 millimeters (3§ inches) withoutencountering any resistance. Several other openings arevisible along the outer wall of the subsidiary tympaniccavity, but with one exception they ail lead into shallowpockets or diverticula. In this single exceptional instancea slightly curved probe can be passed in to a depth of 25millimeters (1 inch). This small curving cavity is situatedin the mass of bone which forms the angle between thetympanum proper and the larger subsidiary cavity, and itsfarther blind end must lie in close proximity to the cochlea.If the opening in the promontory should prove not to bethe fenestra rotunda—and Tick (vide antea) casts a doubtupon this point—l would suggest this curved niche as thenext most likely situation for the fenestra rotunda.

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 tobe of considerable thickness, probably at least 5 millime-ters ( t

3g inch) in diameter. This smaller cavity, as wehave mentioned before, is entirely shut oft' from the tym-panum proper. It is, roughly measured, about 10

ters (|- inch) square, and its height is probably less. Atits highest point, toward the external auditory canal, thereis an opening (diameter circa 4 millimeters) through which

ANATOMY OF THE ELEPHANT’S EAR.

the probe can be passed, in an outward direction, 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 slightly over-towers the head of the hammer; that is, it is a little nearerto the tegmen tympani. There is quite free play betweenthe two ossicles, both of which, however, may be describedas being very solidly anchored in their respective positions.Considerable force may be applied to the handle of thehammer near the umbo of the membrana tympani beforeany visible excursion of the head of this ossicle can be dis-tinguished. 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.

The labyrinthine structures and the relations of the stir-rup to the surrounding parts were not investigated, as itwas found that this could not be done without great risk ofseriously injuring the specimen. If permission can be ob-tained to carry on the investigation, even at the expense ofthe total destruction of the specimen, a further report willbe made in regard to these more intricate anatomical rela-tions.