No. 924.

LONDON, SATURDAY, MAY 15, 1841.

COURSE OF LECTURESON THE

ANATOMY, PHYSIOLOGY, AND DISEASESOF

THE E A R.

By GEO. PILCHER, Esq., Lecturer onSurgery.

DELIVERED AT THE

WEBB-STREET SCHOOL OF MEDICINE,SOUTHWARK.

Arranged and Prepared from NotesBy THOMAS WILLIAMS, M.B., &c., Demon-

strator of Anatomy at the same School.

LECTURE V.

BEFORE proceeding to the examination ofthe organ of hearing in the superior osseousfishes, the general statement may be made,that it presents no very obvious differencesas regards the number and disposition of itsparts, from that state under which we foundit in the cartilaginous division. Like thelatter class, the higher organised bony fishespresent the auditory apparatus in a conditionof comparative simplicity, composed only ofsemicircular canals and vestibule. The sac-cular projection from the sinus communis,constituting, according to some anatomists,the rudiments of the future cochlea, formsthe transitional grade from the uncomplicatedlabyrinth of fishes to that of amphibia andreptiles, in which the cochlea appears.* In apreceding lecture it was incidentally ob-

served, that Treviranus, Weber, Monro, andsome others, among whom Hunter may beranked, had positively described pouches in ithe skin and integument over the situation Iof the ear, which they conceived to standin that relation to the labyrinthic apparatusin the cartilaginous fishes, which the fenestraovalis occupies, in reference to the vestibuleof the higher animals. But in the rays andsharks, in which they can most readily be de-monstrated, the counter-opinion of Blainville,Bell, Scarpa, and Muller, that they cannot,An opinion, the incorrectness of which

will be afterwards proved.

from their anatomical arrangement, and re-moteness from the internal ear, fulfil the pur-poses of an auditory meatus, may be veryconclusively verified. It appears the moreimportant to impress you with a right notionupon this disputed question, since it affects a.fundamental principle in acoustics, that solidsoffer conditions more favourable for the con-duction of sound than liquids or aeriformfluids.

It has already been noticed, however,that in the skates and rays, and others of theplagiostomatous fishes, there is an elongationwhich projects from the inner and uppercorner of the vestibule, and rises into con-tiguity with the common integument, cover-ing the interval between the two eyes. Theextreme end of this prolongation is supposedby some writers to represent the fenestraovalis. Notwithstanding the apparent affi-nity in structure, there are objections raisedby Muller, to considering this as designed toperform the part of an external communica-tion. It is obvious, he states, from thestrength and thickness of the integument of-which it is composed, that the vibrations ofthe surrounding water could not be conveyedwith any greater force through its mediumthan that of the cranial bones. The sup-posed analogous structure with which the

amphibia, living for the greater portion oftheir existence in the water, are provided, isa moveable operculum, covered with musclesand skin, and incapable, according to the ex-periments and imitative contrivances of thisphysiologist, of assisting hearing in water,but calculated materially to improve it inair. If this be the case, it may be thoughtthat the arrangement of this part in cartilagi-nous fishes cannot add much to the intensityof audition.

In osseous fishes there is no fenestral com-munication with the external surface ; nor isthere any trace of a vestibular opening.There are, however, one or two exceptions tothis general law of structure. The informa-tion is given us on the authority of Otto andHeusinger, that in the ear of two species ofthe lepidoleprus, of which little is known,diverticula of the vestibule are observed tobe conducted through corresponding aper-tures in the cranial bones into contact with

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the integument. It has been remarked, that the capacity of the channel within, in conse..in the higher genera of cartilaginous fishes, quence of the disproportionate thickness ofthese productions of the vestibule are so ob- their walls.vious, as to have been by Weber compared This principle of construction, by sensiblyto external auditory canals. This unques- narrowing the cubic surface over which thetionable distinction between the disposition nerve is spread, and correspondently limit.of [the auditory organ in the two classes, ing the extent and amount of the vibratingmust be associated with some equally distinct materials, obviously has for its object to sub-physical law. due the intensity of the rougher undulations.In the soft material of which the skeleton In speaking of the membranous labyrinth of

of cartilaginous fishes is composed, it is ma- fishes, it should be recollected that the coch-nifest that sonorous undulations conveyed to lea cannot be anatomically included; for itthe ear can undergo but little increase, by re- will be subsequently shown, that the suppo-sonance and reflexion, from one wall of the sition of Breschet and Cuvier, which esta.acoustic chamber to another; additional con- blishes an analogy between it and the sacculus,trivances become, therefore, necessary, to as exhibited in the diagram of the lophiusproducethe perfection of hearing. In the pla- piscatorius, is erroneous. The cochlea is angiostomatous fishes this is realised in the appendage to the cartilaginous or osseous,arrangement, by which the auditory sac is and possesses, in its structure, nothing in.

prolonged into more or less immediate com- common with the membranous labyrinth.munication with the integument of the head. The bony labyrinth may have arrived atIt is evident that the inferior and imperfect comparatively advanced perfection, as pre-power of conduction enjoyed by the cartila- sented in the classes of fishes now under ex-ginous skeleton of these fishes, renders a amination, without the formation of an un-provision necessary for bringing the internal equivocal cochlea. The membranous vesti-ear into advantageous communication with bular sacs, ampullae, and semicircular canals,the vibrating element. It is on this account, continue likewise as separate elements of theprobably, that the fenestral-like prolongation auditory apparatus, in reptiles, birds, andof the labyrinth exists in the shark and rays. mammalia ; for in the former, as well as inIn the cyclostomatous fishes, as the myxine the latter, the cochlea may be determined as aand lamprey, the acoustic sacculus, with its chamber superadded to the osseous, and not torudimentary canals, it was formerly stated, is the membranous labyrinth. The incorrectnesswholly imbedded in the cranial cartilage; a of the analogy, therefore, sought to be insti-circumstance which obviously renders the tuted between the sacculus vestibuli of fishes,organ of hearing with difficulty influenced and the cochlea in its rudimentary form, is

by the vibrations propagated to the body and contradicted by the fact of their anatomicalhead of the animal, and therefore explains independence. From this it is evident thattheir imperfect hearing. the pouch sometimes observed upon the

In osseous fishes, however, these auditory sinus communis canalium semicircularium,passages are superseded by the intensity or the sacculus vestibuli, or any other diver-with which vibrations are communicated ticulum of the membranous labyrinth, cannotthrough the solid structures of the body. represent the future cochlea, since the latterThe resonant properties of bone, likewise, by belongs to the osseous or cartilaginous laby-the reverberation and echo which occur in rinth. The cochlea, and its specific orga-the labyrinthic chamber, reinforce the sound, nisation, will, however, be subsequently con.and consequently impress with augmented sidered.effect the auditory nerve. The humours of the labyrinth in fishes re-

It was stated in the preceding lecture, that quire separate attention. In mammalia, it isthe semicircular canals in fishes attained a known that the chambers of the labyrinth areconsiderable size, exceeding those of mam- partitioned off in such manner as to be capa-rnalia and man, alike in length and breadth. ble of containing two liquids, of which oneThe external superficies, however, of the car- occupies the interspace between the membra-tilaginous or osseous canals, form a very fal- nous and osseous canals, and the other fillslacious gauge for determining the admea- the interior of the fmmer. The analogy fur-surements of the membranous canals. In nished us in the mechanism of the higherthe class of fishes the proportional dimen- ears, has induced the supposition that insions of the containing and contained canals fishes, likewise, a similar arrangement mustdiscover few variations ; the diameter of the exist: the grounds of the comparison, how-membranous being one-third that of the car- ever, are imperfect. In fishes, for the mosttilaginous or osseous, in which they are part, the membranous labyrinth constituteslodged: thus leaving a very considerable in- exclusively the auditory apparatus, forterval for occupation by the labyrinthic the cavity of the cartilaginous or osseous

water, or perilymph of Cotunnus. Prose- labyrinth communicates freely with that ofcuting the examination towards the interior, the cranium, apparently removed from eachit will be discovered further, that the mea- other only by the intervention of the arach-sure of surface offered by the membranous noid tunic, or, in some instances, the duracanals externally, forms no correct index of mater. It is thus that anatomists have been

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led to the incomct comparison of whatBreschet has denominated the endolymphcontained in the membranous labyrinth, andthe liquid of Cotunnus, which in the higheranimals De Blainville and Breschet havecalled the perilymph. The anatomical con-struction of the ear in fishes, however, expli-citly points to the encephalic liquid, as thecounterpart of the perilymph of mammalia.It is an opinion, which has long been ex-pressed by Weber and Breschet, that the lin-ing of the cartilaginous and osseous laby-rinth is derived as a prolongation from thedura mater and arachnoid; the former ofwhom further remarks, that even in mamma-lia the delicate vascular lining of the laby-rinth is originally, in the earlier stages of em-bryonic existence, continuous with the cra-

nial meninges.This statement, however, must be received

with caution, since it has been already ob-served, that the organs of sense are formedin instances in which no trace of brain is

present. The lining membrane of the aque-ducts of the more perfect organs, in theirmode of formation, have been thought byMeckel to resemble that of the labyrinthicmembrane: an account supported by Mr.W. Jones, who believes likewise that theinterior of the osseous labyrinth owes itslining membrane originally to a production ofthe dura mater and arachnoid ; which may beillustrated by the example of the processusvaginalis peritonei, when prolonged as a

covering to the testicle.Ear of the Lophius Piscatorias.

Fig. 4.

(a) Sinus communis. I(b) Sacculus rotundus.(c) Posterior canal. ’

(d) Anterior canal.(e) External canal.(t AmpuHae.(tT) Utricle.(h) Nerve.

The acoustic nerve presents no peculiarityin its distribution in fishes, excepting that inthe instances of its continuation by meansof slender filaments, inwards as far as thesurface of the otolitic mass. It proceeds ina separate form from the medulla oblongata,

at its posterior and inferior portion, emergingevidently by that sulcus on the lateral partof the medulla which intervenes between the

olivary and restiform bodies, and which, iftraced inwards, would lead into the fourthventricle; thus corresponding, in its anato-mical characters, with the portiomollis in thehuman subject.* In proportion as it ap-proaches the ear, the nerve undergoes divi-sion into branches, of which some, reducedin size, proceed towards the ampullae of thesemicircular canals, the remaining beingseen to spread themselves over the sacculusand vestibule.

In many fishes it is not difficult to showthat delicate fibrillae from the nerve continueinwards, to connect themselves to the calca-reous otolites, by means of a groove, pro-vided on the convex surface of these bodies.There is some ambiguity in the significationof this arrangement. Roget exemplifies theprinciple of its operation in the work of

hearing by the clapper of a bell, to whichhe supposes them to perform an analogousoffice. The acoustic purpose of this peculiarcontrivance, however, is rendered still moreobvious, by an experiment of great simpli-city performed by Camper: he filled a smallbag with water, and placed within it a smallglobular body, which, of course, from its un-

attached freedom, was capable of rolling inany direction, according to the force of anexternal impulse. Sustaining the apparatusin the hand, he found that the slightestagitation given to the bladder was 1’epeat-edly felt by the reaction of the body within.The vibrations, then, of these masses exist-ing in the ear of fishes, probably aug-ment the intensity of hearing not so muchby reverberating from wall to wall in thelabyrinthic cavity, as by direct propaga-tion along the filaments of the auditorynerve attached to the surface of the vibra-ting body. The masses of caZCa1’eous mattercontained in the interior of the labyrinth,surrounded by the endolymph, of whichwe have spoken, according to some, arediscoverable in all classes of animals, fromthe vestibular ear of crustacea and fishes,to that of the human subject. These creta-ceous substances amount, for the most part,to three in number, and are found within thevestibular sacs, and its communicating smallersacculi. In density they present variationsaccording to the class of fishes in which theyare examined. In the cartilaginous, as for-merly stated, they assume a pulverulent, andsometimes crystalline, appearance, and aresoft and pulpy in consistence.

In the osseous fishes they acquire a petrousdensity proportionate to the perfection of theossific structure of the animal’s skeleton, thatis, the more complete the transformation of

the cartilaginous into the bony skeleton inthe series, the greater the density of these

J See diagram.

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otolites. In figure and size they also vary,according to the species. In some, as thesalmon, they are incurvated like the valve ofa shell. The chemical constitution of thesesubstances, as conveyed by the terms, calca-reous and osseous, so frequently employed,appears to be made up of common compo-nents ; differing from that of ordinary bone inthe proportion of phosphate of lime, which inthese bodies is small. The analyses ofHuschke and Barruel determine their ingre-dients to be, carbonate and phosphate oflime and mucus, in addition to which alittle animal matter was made out. Theseconcretions, when discovered in the semicir-cular canals, are confined to the ampullas.In fishes it is plainly shown, by the accom-panying sketch of the labyrinth and otoco-nies,* that the proper situations for the lodg-ment of the latter are the common sacculus,the utriculus of the sinus canalium commu-nis, and the pouch of the vestibular sac

called the cysticule. With these situations

Membranous Canals of Lophius Piscatorius.Fig. 5.

(a) Ampul1ae.(c) Cysticule.(s) Sacculus rotundus.(n) Branches of nerves.(o, o, o) Otolites shown in outline by dotted lines.

a coincident disposition of the branches of thenerve is remarked, a considerable divisionbeing implanted on the external surface atpoints corresponding to the resting-places ofthese otolitic masses. The error has beencommitted of comparing these substances inacoustic properties to the tympanic ossicula.From the peculiar principle of adjustment,however, evinced in these delicate elementsof the auditory apparatus, floating as hydro-static balances in the humour of the cavity,they are admirably calculated to reinforcethe sonorous undulations within the acousticchamber. The office of the tympanic chainof bones, is the conduction of the sonorousundulations from the external to the internalear.

It is to Professor Weber that we are in-debted for the discovery of a communicationbetween the air-bladder and the labyrinth in

* Qroe, auris; OVLl;., pulvis.

bony fishes. From this statement it is not tobe inferred, however, that the aeriform con.tents of the swim-bladder have a - ee andundivided communication with the cavity andcontents of the labyrinth. This, indeed, wereto make grounds for the revival of an ex-ploded and antique theory of audition, pro-pounded and recognised in the days of Fallo-pius, Eustachius, and Duverney ; accordingto which the faculty of hearing was dependentupon the agitations of some occult principle,or subtle and innate air, aer ingenitus, thatpervaded the various windings of the laby-rinth. Diogenes, and even the observantAristotle, gave their admission to the exist.ence of this aer ingenitus; and it was notuntil the more enlightened labours of Domi-nico Cotugno that the precise mechanism ofthe labyrinthic chambers, with their separatehumours, was conclusively shown.*The orders of animals to which our ascen-

sive method of study leads us next to exa.

mine, are the Amphibia and Reptiles.

* [The connection which exists betweenthe air-bladder and the ear is established, inthe greater number of instances, by the inter-medium of a chain of small bones. Thisbony junction is seen in all the species of thegenus cyprinus or carp ; in the silurus,including some electric varieties; and like-wise in the cobitis fossilis, or loache. Inthese examples the communication is esta-blished by means of a series of ossicula, articu.lated, according to Weber, with the three firstvertebrae, and in contact posteriorly with theair-bladder. They are so definitely arrangedbetween the labyrinthic membrane at one

extremity, and the air-bladder at the other,as to have suggested a comparison betweenthem and the tympanic ossicles of mammalia.The analogy has been extended into the sup-position, that the air-bladder performs thesame part to the ear of these fishes, with thatwhich, in the higher animals, devolves uponthe membrane of the tympanum. The firstvertebra is situate in close approximation tothe ear, and presents on its transverse processa foramen or sinus, in which the ossicle, cor-responding to the stapes in mammalia, is

lodged; the malleus, at the other extremeof the chain, being in contact with the air-bag. In other fishes, however, the commu-nication between the auditory organ and theair-bladder is accomplished without the inter-medium of bones. The herring presents uswith an example, in which the bladder is

prolonged anteriorly into a tubular sac whichbifurcates, and extends into contact with thelabyrinth through appropriate apertures inthe occipital bone. In some genera of fishes,the connection is established indirectlythrough the intervention of the encephalicliquid. Other differences are found in themode in which the ear is made to communi-cate with the air-bladder.-T. WILLIAMS.]