The endings of the nervus acusticus in the labyrinth of the carp

{From the Zoological and Biological Institute of the University of Szeged. Director: Prof. A~rBROSIUS ABRAHam[.)

T H E E N D I N G S OF T H E NERVUS ACUSTICUS IN T H E L A B Y R I N T H OF T H E CARP.

With 16 Text Illustrations.

By AMbrosias A~RAHXM.

(Received, October 11, 1949.)

1. The structure of the membranous labyrinth of the carp.

The labyrinthus of the carp is a membranous labyrinth (labyrinthus membranaceus), agreeing as regards development and structure with the sense organs of the other vertebrate animals serving a similar purpose. Essentially it is composed of two diverging parts which are, however, closely connected with each other, namely an upper anterior and a lower posterior part. I t s anterior or rostralis part is the utriculus and the communicating semicircular canals, the posterior or caudalis part is the sacculus and the lagena cochleae, the latter involving the greater p~rt of the area of the primer sacculus.

The utriculus is an elongated tube laterally compressed, its main bulk being constituted by the anterior, vesicularly extended, fairly well circumscribed recessus utriculi adjusted into a small groove of the interior surface of the prooticum. I ts middle narrowing part is the utrieulus proprius, its posterior blind-end the sinus posterior: From the upper hind par t of the utriculus arises the sinus utriculi superior ascending in the shape of a tube relatively wide in diameter vertically upwards along the synchrondrosis formed by the vertical lateral plate of the prooticum and occipitale, ending in the utriculus of the small apex sinus superior.

On the anterior end of the recessus utriculi the ampulla rostralis is situated which gradually widens and proceeds into the canalis membranaceus semieireularis rostralis. The latter ascends in the vertical

A. Abraham: The Endings of the Nervus Acusticus. 397

plane in the fossa auditiva of the prooticum presently leaves it, bends backwards in the cavity of the skull before the upper part of the prooticum, and epioticum, describes a semicircle, widens to a small ex tent - - immedia te ly under the apex sinus superioris--and finally runs into the upper end of the sinus superior.

The upper edge of the recessus utriculi bears the ampulla lateralis, which agrees in shape with the ampulla rostrahs, but for it being far smaller than the latter. The ampulla lateralis gets gradually thinner and passes into the canalis membranaceus semicircularis lateralis which runs in the horizontal plane. The latter also runs forward for a certain distance in the fossa auditiva beneath the canalis semicirculacis rostralis presently, however, it leaves the cavity of the skull and enters the corresponding canal of the pteroticum, in which retaining its horizontal plane it bends in the direction of the caudalis, subsequently passing into the epioticum and from there into the occipitale laterale from which it emerges into the cavity of the skull and goes with its moderately widened end into the utriculns proprius.

The posterior par t of the utriculus proprius bears in a small groove, constituted by the oecipitale lateralis, the ampulla caudalis which is even slightly smaller than the ampulla lateralis and gives rise to the canalis membranaceus semicircularis caudalis. The latter enters over the foramen nervi vagi into the vertical lateral plate of the oceipitale laterale proceeding in the same canal as the canalis semicircularis lateralis. The canalis membranaceus semicircularis caudalis runs in the wall of the skull towards the cavi ty of the skull ascending presently vertically, in the interior of the bone, in a curve, into the epioticum, from where it emerges from the top of the roof constituted by the epioticum and runs, descending slightly in the cavity of the skull beneath the apex sinus superioris, into the sinus superior. The base of the utriculus has a small oval aperture which gives rise to the ductus utricolo saccularis, the latter connecting the utriculu-s with the sacculus.

The sacculus which constitutes the posterior part of the labyrinthus membranaceus and the lagena cochleae is s i tuated in a quite seperate part of the cavity of the skull, in the bulla lagenaris, constituted by the body of the basioccipitale and arched over by the horizontal medial plate of the occipitale laterale.

The sacculus is a small tube running backwards and slightly downwards consisting--as generally the sacculus of the carp like fishes do- -of an anterior, median and posterior section. At the boundary of the anterior and median sections the ductus utriculosaccularis enters into it. From the lower part derives the ductus endolymphaticus, turning first a little backwards and upwards then bending gradually over, it runs along the sinus superior, following the latters direction, its end being blind.

Z. f. Zelfforschung, 35. Bd,, Heft 5/6. 26

398 A. ~brahdin :

The median section is characterised by the septum longitudinale sacculi, which divides this section of the sacculus into a dorsal and a ventral cavity. The dorsal cavity communicates through the canalis communicans transversus with the sinus impars into which the canalis transversus of the other side opens into. The continuation of the sinus impars are the two atria sinus imparis, to which the first bones of WEBER'S boneduct are adjoined. The ventral cavity communicates with the posterior part of the sacculus.

The wall of the sacculus lateralis, near the posterior section, bears a round aperture leading to the lagena cochleae. The tube starting from the aperture is the canalis sacculolagenaris. The lagena is an oval laterally compressed big vesicle situated outwards, upwards and backwards from the sacculus. The lagena and the lateral wall of the sacculus are so closely attached to each other that actually the wall dividing the two cavities appears to be united. The wall is pierced by the ductus sacculogenaris. At first sight, on studying the prepared labyrinthus of the skull, grayish-whitish spots of different size and shape strike the eye, these are the stones of the hearing organs of the bone fishes, the so-called auditory stones, the otoliths, which are already known to science since a fairly long time. In the labyrinthus of the carp there are usually, not considering some small and not constant accessory stones, three larger stones: one in the utri~ulus, one in the sacculus and one in the lagena. The recessus utriculi of the utriculus contains the oval not very extensive, convex, concave lapiltus; the saeeulus, the long, thin, pointed three adged sagitta and the lagena, the large oval, flat asteriscus, which has an incision on one edge. The asteriscus bears rings indicating growth, by their number one can tell the age of the carp. The thin stem of the sagitta of the sacculus is embedded in the gelatinous substance of the pars caudalis, its anterior end, situated in the middle area of the sacculus, is three edged. Some investigators hold the view that the three edged sagitta rotates in the endolympha, hke a millwheel suspended on both ends, being capable of intercepting the vibrations arising from the different impulses.

According to all heretofore made statements the membraneous labyrinthus is exclusively innervated by the nervus acusticus. The nervus acusticus of the carp is very short and divides immediately after emerging from the medulla into two branches. One of the branches is the ramus anterior which divides before long into three branches. These are the ramulus ampullae rostralis, the ramulus ampullae lateralis and the ramulus reeessus utrieuli. The second branch is the ramus posterior its branches are the ramulus sacculi, the ramulus lagenae and the ramulus ampullae caudalis. Besides these, at the branching of the ramulus lagenae and the ramulus ampullae caudalis there arises still

The Endings of the Nervus Acusticus in the Labyrinth of the Carp. 399

a small nerve branch which is called ramulus neglectus which in turn soon divides into two smaller branches.

At the endings of the nerve branches described above we find the sensulae. These are different sized bulges of the wall of the labyrinthus representing those parts of the auditory system which percieve and convey the impulses. They are generally defined by the nomenclature according to their shape and denoted as crista and macula respectively. The labyrinthus of the carp contains three eristae: the crista acustica ampullae rostralis, the crista acustica ampullae lateralis and the crista acustica ampullae caudalis. There are five ,maculae: maeula acustica recessus utrieuli, macula acustiea sacculi, macula acustica lagenae and the two maculae acusticae neglectae. These are formations which accomodate in their specially formed epithelial cells the endings of the acusticus, their apparatus perceives and transmits the different impulses ensuing from the movements of the endolympha situated in the labyrinthus nlembranaceus.

2. The problems.

Earlier investigators, particularly HASSE, KUgN and RETZIUS and others studied very intently the structure of the sensulae, however, owing to their primitive methods, poor knowledge of neurohistology and lack of adequate nerve-technic they did not succeed in gaining insight into these complex apparatuses. The same can also be applied to recent investigators, who using the generally employed fixation and staining methods of histology instead of achieving progress, on the contrary, rendered the problems still more obscure accumulating on this subject in the literature doctrines which were f lom the point of view of neurohistology untenable. This is of course not astonishing as the technical solution of the question is also from the anatomic point of view very difficult, but the difficulties increase to a great extent on at tacking the problem without having adequate technical knowledge and even to a still greater degree in the absence of satisfactory foregoing neurological studies.

Perhaps these facts offer an explanation for the conclusion reached by the author on surveying the literature relating to this t heme- -a s far as it was available to h i m - - t h a t no efficient examinations of the sensulae of the bone fish have been stated ; so that everything he succeeded in establishing concerning the labyrinthus and nerve connexions of the carp, and through it of the bone fishes in general, can be considered as a new contribution to the hterature. As, considering the nature of the matter , the author was only interested in the nerve connexions, his at tention was focussed on their deficiencies. Thus, in the following description only the structures of the sensulae and nerve branchings leading to them will be dealt with in the manner it became possible to

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400 A. Abraham:

establish them on the section series and nerve preparations from the labyrinthus of the carp.

3. Material and methods.

The investigations were exclusively carried out on the carp (Cyprinus c/~rpio L.). For these examinations very many carp heads were needed always supplied gratuitously, inspired by his esteem of science, by Mr. GY. FffLDP, the proprietor of the "Fiil6p Css in Szeged, to whom the author is very indebted and desires to express his gratitude once more, without his kind support it would not have been possible to procure this expensive material on which also investigations in other directions were carried out in the institute, the more so since for these studies of course very many carp heads were used.

The labyrinthus was dissected from the freshly obtained carp head without any foregoing treatment, or after having been fixed in form- aldehyde. On such anatomic preperations the different sections of the labyrinthus and their connexions could be fairly exactly detected. During this work we made very good use of the communication of I~nTZ~US dealing with the labyrinthus of the Cyprinus Idus L., the splendid drawings of which were most helpful for the elucidation of these complex questions. The otholiths were removed from the prepared labyrinthus and part of the material gained in this manner fixed for adequate histological studies, it was embedded and series of sections were prepared which were stained with ferrohaematoxyline and eosine. These series enabled the investigation of the situation and histological structure of the different components of the labyrinthus, but particularly as regards the shape, position and histological structure of the sensulae. Naturally these pictures do not reveal any nerves, not even in traces, with the exception of one or two phenomena which have also already been observed after similar procedures by others, proving, however, to be quite worthless without neurological investigations.

For the neurological investigations the material was fixed in form- aldehyde and partly stained by the BIELSCHOWSKY method and its modifications and partly by a new not yet described method of mine. Frozen sections were exclusively used exhibiting with the help of post- gilding, or without it, in a most satisfactory manner the nerve connexions of the sensulae and the structure of the nerves, ganglia and nerve cells. Several hundred preparations were made of the ampullae, the utriculus, the lagenae, the sacculus and the nerves and ganglia leading to them, on most of them the structure of the sensulae, the ganglia and the nerves is most clear and distinct. All these nerve eonnexions will be dealt with in detail below, first the structure of the cristae, then the nerves leading to them and finally the maculae.


4. The structure of the cristae.

The crista acustica is a body bulging out of the wall of the ampulla, it sinks fairly deeply into the lumen bearing on its end, which consists

Fig. 1. Cyyrinus cavpio L. : Crlsta acustiea. BI]~LSCI~OWSKY method , a neuroepi the l ium, b ne rve ter~ minat lons , c t he ne rve of the crista, d l amina propria , e epi thel ium, f suleus t ransversus . Microscopically

200 • magni f ied , photographical ly d iminished to the a/a-

of the, at the base slim proximally bulging membrana propria, a relatively thick epithelial-cap (Fig. 1). On its base, at the point where it bulges out from the wall of the labyrinthus it has an incision, the sulcus transversus, over which the lamina propria exhibits a saddle-like folm. On

402 A. Abraham :

its side the one layered flat epithelium of the ampullae proceeds, being here a somewhat higher, rather more a kind of singly layered cube epithelium, but not infrequently it runs on the one side into a high cylindrical epithelium, whilst on the other the cubic epithelium remains. Its base, particularly in the area of the suleus transversus, is limited by a layer of connective tissue consisting of relatively broad and thick collagen fibres which are wavy and run parallel. Between the fibres there are many gaps in the connective tissue containing numerous praecapillary arteries and capillaries. The greater portion of the substance of the crista is that essential substance which is but the column-like continuation of the lamina propria of the labyrinthus membranaceus. The lamina propria is a peculiar, homogenous, cartilage-like substance showing great chemical affinity on the action of basic aniline dyes and containing fairly many capillaries often constituting, principally in the area of the utriculus and the lagena, a dense fusing system. The endothelial cells can be easily detected in the single vessels of these systems as can be the typical, longish, nuclear red blood cells in the lumen. The capillaries of the area of the crista run in various directions those, however, making direct for the epithelial-cap mostly proceed parallel. The structure of the capillaries exhibits the typical capillary structure, so that the author even succeeded in impregnating in the utriculus area an associated sympathetic nerve fibre running parallel to their lumina. As was cited above the lamina propria is a homogenous substance containing numerous thin canals without preformed wMls running in all directions, which are undoubtedly functionals of the circulation, hence of the nourishment and excretion. The longish cavioties have pointed ends and cells resembling bone cells. Furthermore the following peculiarity must still be reported: in the area where the epithelium, limiting the stem of the crista, proceeds into the epithelial of the cap a special epithelimn form can be detected consisting of large polyedricM cells which are sharply limited from one another and have a round nucleus. Between these cells in the area where several polyedrical cells face each other, there are smaller, thinner, polyedricM cells too. This phenomenon was also observed by earlier investigators who could not either offer a satisfactory explanation for it. The roof and partly the side of the crista bears the sensula a thick epithelial layer which at first sight, owing to its numerous nuclei, appears to consist of several layers. The structure of this epithelium has been much investigated, however, the following reasons have prevented its elucidation. Above all, even on the thinnest and best stained histological preparation it cannot be quite exactly analysed, furthermore these preparations are full of large, thick, homogenous, columns and strikingly regular wall less cavities which are uninterpretable by the means of modern technics without neuro-


histological examinations. These cavities, tubes and columns have also mislead recent investigators being thus the source of numerous irrational explanations and theories. In spite of these difficulties, however, in general it can after all be-established that the erista cap is a genuine sense epithelium from the uppermost cells of which, the hair cells, there protrude at the roots thick and at the ends thin hairs which on fusing continue in the slender, mucous cupula terminalis extending with its closely interlocking finely granulated mucous fibres deep into the lumen of the ampulla.

The hair cells are longish cells which have big nuclei and are rounded off at the base constituting only the upper part of the thickness of the epithelium. The lower more extensive par t consists of many small, longish ceils with spheric nuclei. These are the long, slim, sustentacular cells extending from the lamina propria till under the hair cells some of them even protruding through the gaps of the hair cells to the surface. This epithelium, contain_ing numerous of the above mentioned tubes, columns and cavities of various shapes has an identical structure on all the cristae. As the head of the crista is very broad it can ~lready be established with the naked eye that the ramulus ampullae leading to it divides, joining it in the form of two separate nerves. Such a case could also be observed in the ampulla caudalis of the pike. The author has also frequently noticed something of the kind in the crista of the ramulus ampullae rostralis and of the ampulla caudalis of the carp. On seeing the branching he thought that this is actually a double crista, but the histological studies reve~led tha t it is only a single one, its head being, however, almost twice as broad as that one of the crista which the ramulus ampullae attains undivided. Most of the sustentaeular cells extend with their upper end to the free surface of the epithelium and with the other till the lamina propria. Usually they spread over the whole neuro-epithelium being as long as the epithelium is thick. SCnVLTZE distinguishes a basement cell-row which does not reach the surface of the epithelium.

5. The nerves leading to the eristae.

The two anterior cristae already receive their nerves from the ramus anterior. The ramus anterior is a flat, broad nerve, well visible to the naked eye. I t s bot tom closely adjoins longitudionally the wall of the reeessus utrieuli, proceeding closely beside it forwards it gives off a branch to the macula reeessus utriculi and then divides into two branches one of which supplies the crista ampullae rostralis, the other the crista ampullae lateralis with fibres.

At the root of the ramus anterior there is a big, longish, flat ganglion, the ganglion vestibulare, its cells are of bipolar type (Fig. 2). One of

404 A. Abrahs :

the processes deriving from the cells runs proximally and the other peripherally. Some of the ganglia cells are unproportionately big, the others are smaller. The size of the cells diminishes gradually towards the periphery of the ganglion, so that at the end of the ganglionMbnt

Fig. 2. Cy~rinus earpio L. The ne rve of tile crista. BmLSCHOWSKY method, a gangl ion cells, b ne rve f ibre , c neurofibri ls . Microscopically 1240 :: magni f ied , photographical ly diminished to the ~/a.

in some places also in the middleMthere are only qui te small cells, with spheric nuclei. These cells are also bipolar and have extremely thin processes. The processes of the big cells are very thick, myelinated fibres, proceeding straight along the ganglion without arborizing (Fig. 3). Around the cells there are different sized nuclei investing the cells like a sheath, although the extremely small number of these nuclei seems


to contradict the presence of a sheath. As a pecularity the fact should still be alluded to tha t occasionally also cell shapes can be detected which decisively look as if they were multipolar cells, however, as, as yet never having been successful in tracing them for a longer distance the author does not dare to risk the s ta tement of the ganglion containing--part icular ly

Fig. 3. Cypcinus ca~p/o L. The nerve of the crista. B~SCHOWSKY method, a ganglion cell, b nerve fibre, Microscopically 400 .< magnified, photographically diminished to the 1/a.

at its borders--mult ipolar nerve cells (Fig. 4). For the rest it is still of interest to mention the forms and distinctness of the neurofibrils of the ganglion cells, particularly those of the larger ones- as an a lmost unique phenomenon-anything similar having as yet never been observed elsewhere. There are big bipolar cells the two big processes of which can be splendidly detected, furthermore one also sees most clearly the falling of the fibre into two fibrils in the cell which proceed loosely through the cell to fuse presently still within it ~t the opposite pole (Fig. 5) and continue in the peripheral process. In the processes themselves, in the

406 A..~brah~m :

Fig. 4. Cyprinus carpio L. Ganglion of the crista nerve. BIELSCHOWSKY method, u nerve cell, b nerve fibre, e neurofibrils. Microscopically 900 magnified, photographically diminished to the 1/2.

vicinity of the cell, the fibrils are not visible, but in the peripheral thick fibres running in the proximi ty of the sensulae and even in the sensulae the neurofibrils appear sometimes most distinctly.

I n most cases it can undoubtedly be established tha t the neurofibrils are present in the cells in which they sometimes exhibit quite peculiar

The Endings of the Nervus Acustieus in the Labyrinth of the Carp. 407

shapes, there are, however, also other cases in which we find ourselves most decidedly face to face with pictures exhibiting a situation where apparent ly the dense fibril plexus is not in the cell, but encloses the cell. I f this would really be the case, it would mean that there is a neurofibril contact, i. e. a nerve ending, and in this case the recently arisen morphologically supported question of the double innervation would actually

Fig. 5. Oyprinus earpio L. Gangl ion of the crista nerve. BIELSCHOWSKY method, a nerve cell, b nerve fibre, e neurofibrfls. Microscopically 1200 • magnif ied, photographically diminished to the 1/2.

be proved. In this case namely it can most decisively be assumed tha t some sympathet ic fibres end here transmitt ing the impulse in the above cited manner, which would mean tha t the double innervation of the hearing organ is actually firmly supported.

To elucidate this question more thoroughly the best impregnated preparations were examined under very high power magnification and in the course of these examinations cells could be detected which seemed indeed to be invested by a neurofibril capsule. Namely it could be established beyond doubt on the microscopic picture tha t a nerve fibre bearing different sized varices proceeds to the cell, falling directly at the border of the cell into three branches which in turn divide after having proceeded for shorter or longer distances. The branches arising

408 A..~brah$m:

in this manner intermingle towards the periphery of the cell so tha t a genuine plexus forms enclosing the whole cell. This picture undoubted ly shows tha t we are dealing with the ending of a dis tant fibre which is a pericellular plexus, or is a t tached in the form of a pericellular net to one of the cell~ of the ganglion. This seems also to be supported by the fact t ha t on using appropr ia te ly the micrometer-screw we a lways

gain the impression of the whole cell-body being actually within a dense neurofibril plexus in a true neurofibril basket (Fig. 6). The difficulty, however, lies in the fact of this cell not exhibiting any process, so tha t we cannot feel sure if we are dealing with an ending of a strange fb re , or if the cell is really only a regular bipolar cell of the ganglion and only one of its processes is visible. In this ease namely it can be assumed tha t the other process is cut off and the position of the neurofbr i l plexus is no t pericellular, but tha t it is in the plasma. Anybody having ever dealt with such questions is acquainted with the difficulties arising every time one wants to reach a decision as to whether the nerve fibres, or neurofbr i ls are on the cell or in the plasma. I f namely there are no transsection experiments at our dis-

Fig. 6. Cyprinus carp/o L. Nerve cell from the posal we are in every such case eom- ganglion of the crista. B~LSCHOWSKY method, pletely dependent on the micro- Microscopically magnified 1240 , , photo-

graphically diminished to the 2 / 3 . meter-screw and by its u s e w e

must in each special case through the simultaneous sharp adjus tment of the nucleus establish what position the nerve elements in question take up. Albeit this criterion is not sufficient to settle this question in a reassuring manner, not even if the query only concerns the establishment of the existing connexion between a nerve fibre, a gland cell, or even only a muscle cell, and the epithelium cell. But we meet the same difficulties in the case of the sympathe t ic ganglia, even if the physiological experiments support the assumption of the preganglionic fibres, or at least most of them, really terminat ing in this part icular ganglion.


For the rest, those ganglionic cells of the acusticus also favour the pericellular plexus conception which are joined on the microscopic picture from the same direction by two, instead of by one, fibres (Fig. 7). These fibres also ramify and get at tached to one another forming such a lucid pericellular plexus leaving hardly any doubt as to the fact tha t we are really dealing, as in the case of some sympathet ic ganglia, with a plexus in which the entire cell-body is enclosed. Nevertheless, in spite of this, this question must apparently after all be dealt with from a different line of approach, as contrasted with these not hundred per cent decisive data,

Fig. 7. Cypr~nus carplo L. Nerve cell from the ganglion of the crista. BmLSCHOWSKY method. Micro- scopically magnified 1240 x , photographically diminished to the ~/a.

i t can in most cases be quite obviously established that, for all that , we are not dealing with a pericellular plexus, but with an intracellular net. This view is supported by those cells in which both processes are visible which are for the rest in every case homogenous, exhibiting very distinctly the intracellular neurofibril network which is morphologically joined to the two processes of the cell (Fig. 8). All this is also very well illustrated on Fig. 9 which amongst others is of great interest because it not only exhibits the apparent a t tachment of the fibres to the nucleus, but also tha t of the nueleolus (Fig. 9). This and similar pictures appearingin far greater numbec than those shown on Figs. six and seven indicate most decisively that the ganghou does not contain strange endings, as it hardly can be supposed tha t - -a l though this is also not quite impossible--one cell of the same ganglion would be at tached in the above described manner, and yet the others would exhibit the generally known bipolar type. I f this would be the case then as there are no preganglionic and post-

410 A. Abrahs :

ganglionic fibres, the structure of the ganglion would in no way justify the supposition of the nerves of the sensulae--not even their especially

thin and characteristic fibres--being elements of vegetative origin. Con- sequently as these are lacking it is not possible to accept on this base the double innervation.

The course of the fibres of the ramulus ampullae is wavy and on traversing the crista lamina propria, most of them are strikingly thick there are, however, also quite thin one~, among them resembling strongly with their smooth edges and thin longish varices sympathetic fibres (Fig. 10). As, however, except for what has been said, respectively, except for the apparently periterminal neurofibril plexus there is no other morphological basis to justify their classification as sympathetic fibres, we cannot on these grounds consider the sensulae to possess a vegetative innervation. For the rest this question will still be treated later.

The fibres of the ramulus ampularis widen gradually beneath the neuroepithelium then thicken strikingly, enter subsequently into the epithelium and attain a thickness, mainly in the middle section, which is almost the manifold of the original one. The thickening still increases at the branching point of the fibres, reaching in this case a degree, as yet unknown in the sensory end-organs. In most cases

Fig. 8. Cyprinus carpio L. Nerve cell f rom the t runk stumps develop being five-six ganglion of the erista. BmLSCHOWSKY method, t i m e s a s th ick--or even still th icker-- Microscopically magni f ied 2700 , photo-

graphically diminished to the 2/a. than the diameter of the fibre (Fig. 11). The empty places of these nerve pieces,

resembling stumps of tree trunks with roots afford those peculiar pictures exhibiting on sections obtained by the usual microtechnical procedure and staining, the already above described columns, spherical and elliptical

The Endings of the Nervus Acusticus in the Labyrinth of the Carp. 41I

cavities which the more recent literature--based on various speculations~-- refers to, as to the lacuna system. The nerves, particularly at the branching of the ramulus ampullae, as can also very frequently be observed in the case of the ampulla rostralis overspread in such great masses the epithelium nothing of the kind having as yet been observed in the epithelium of any other sensory organ by the author (Fig. !2). For the sake of com- parison the labyrinthus of the dog and cat were investigated and it was established that the similar sections of their labyrinthus contained far fewer

Fig. 9. Cyprinus carpio L. Nerve cell f rom the ganglion of the crista. BIELSCHOWSKY method . Micro- scopically 900 ~ magnif ied, photographical ly diminished to the 2/a.

nerves than the sensulae of the carp. The epithelium is indeed quite full of nerve fibres which is especially well visible on pictures representing the exact transsection of the epithelium.

The remarkably thick pieces of the intraepithelial of the thick nerve fibres start to arborize approximately in the middle of the epithelium, their branching is so rich that it is quite fluitless to at tempt its repro- duction on drawings, but even its description remains but a faint imitation of a nerve picture which can be well traced and examined in its integrity.

The thick branches emerging from the similarly thick endstumps proceed first in the middle of the epithelium towards the right, respectively the left borders of the epithelium carp. The branches are so numerous that they practically touch. These branches give rise to more and more branches proceeding in all directions and turning the lower two-thirds of the neuroepithelium into a genuine nerve tissue. The thinner branches are in close connexion with almost every part of the sustentacular cells and proceeding presently towards the surface communicate with the hair

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cells. The fibres running towards the cells si tuated in the vicinity of the lumen ascend quite high, indeed it is not rare tha t fibres, deviating from

Fig. 10. Cyprinus earpio L. The fibres of the crista nerve. BLELSCtlOWSKY method. MicroseopicaUy 900 ~: magnified, photographically diminished to the 1/~.

The Endings of the Nervus Aeusticus in the Labyrinth of the Carp. 413

all preceding observations, end in the open, quite on the surface in the line of the boundary of the epithehum in the form of small end-knobs, or small spoon-like plates (Fig. 13). Other fibres only reach the base of

Fig. 11. Cy~rinus carpio L. Cris ta acust ica. BIELSCH0WSKY method , a ne rve f ibres , b l amina propria, c ne rve temnihal knobs, d neuroepi thel ium, e ne rve te rmina t ions . MieroscopicaUy 600 • magni f ied ,

photographical ly d iminished to the l/2.

the hair cells or its nucleus widening there into a plate adjoining the plasma of the cell. These endings of the surface of the epithelium, furthermore the fine branches terminating in the hair cells and the thick fibres in the epithehum in general, are undoubtedly sufficient and suitable for

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414 A..~brahs :

the bringing about of an inner contact between the epithelial cells and the nervus acusticus, simultaneously being most appropriate to render

Fig. 12. Gyprinus carpio L. Cris~ acustica. BIELSCIIOWSKY method, a nerve fibre, b nerve terminal knobs, e int raepi thel ia l nerves, d nerve terminat ions, e neuroepithellum. Microscopically 620 • magni-

fied, photographically diminished to the 1/2.

the whole apparatus highly suitable for the reception and transmission of the impulses reaching it via the eupula terminalis and the endolymph.

The Endings of the Nervus Acu~t~cus in the Labyrinth ol the Carp. 415

The ramulus ampullae eaudalis supplies the crista of the ampullae caudalis with nerve fibres which is a branch of the ramus posterior. The terminal conditions of the ramulus ampullae posterior are similar to those of the fl'ontal cristae precedingly described.

Fig. 13. Cyprinus carpio L. Crista acustica. BYELSCHOWSKY method, a ne rve t e rmina l knobs, b lntra- epithelial nerves , e neuroepi thel inm, d nerve terndnat ions . Microscopically 1000 • magni f ied , photo-

graphical ly d iminished to the 1/~.

6. The structure of the maculae.

After having described the structures of the cristae we must deal with those of the macula acustica recessus utriculi, respectively with its innervation conditions. From its base ascends, like a not sharply defined

27*

416 A. /~brahAm :

diffuse spot, the macula utricuh. This is essentially a pecuhar epithelium composed of two layers agreeing in structure entirely with the epithehum of the cap of the crista. The cells around the lumen are also in this case limited by hair cells with processes, underlying them there spreads out a thick layer of longish sustentacular cells composed of one layer in which the nuclei can be located in different altitudes, thus the

Fig . 14. Cyprinus carplo L. Macula utriculi. Nerve plexus of the neuroepitheliunl . BIELSCHOWSKY method , a ne rve f ibre, b the nuclei of the epithelial cells. Microscopically 600 < magni f ied , photo-

graphical ly diminished to the 1/:.

epithelium seems to have the form peculiar to manifold epitheliums. This epithelium proceeds at the border of the macula into a cyhnder epithelium composed of a single layer the continuation of which is the cubic epithehuln lining the cavitty of the utriculus. Both kinds of epithelium rest on the lamina propria composing the bulk of the wall of the utriculus, which is externally joined by a lattice structured connective tissue layer having abundant blood vessels. The structure of the lamina propria is similar to that of the ampullae areas, it only differs inasmuch as it contains more capillaries and is also perforated by many holes of valious size and shape--circular or oval-- through which the nerve bundles enter the macula. The ramulus utricularis innervating the macula


ntriculi is one of the branches of the ramus anterior the lat ter adhering flatly to the wall of the utriculus. This branch falls directly beneath the lamina propria into numerous bundles which enter through the apertures of the lamina propria into the epithelium of the macula, in which the branches thicken composing an almost inpenetrable plexus (Fig. 14). The fibres of this thick plexus begin then gradually to arborize by also thickening at the branchings in the same manner as the similar termina-

Fig. 15. Cyprinus carpio L. Nerve plexus in the ep i the l ium o f t he macu la utriculi . BIBLSCHOWSKY method , a ne rve f ib re , b neuroepi thel ium, e the nuclei o f the epithelial cells, d n e r v e t e rmina t ion .

Microscopically 900 • magn i f i ed , photographical ly d iminished to the 1/3.

tions of the cristae do, although they do not thicken as extensively as those in the epithelium of the cristae. Presently the thick nerve stumps arborize richly and compose a very abundant plexus in the median section of the epithelium. From these plexuses there emerge delicate single fibres which are also in close connexion with the sustentacular cells and hair cells. These connective conditions can generally be well studied, however, owing to the abundance of nerves and to the ever increasing preparation difficulties, the relation between the single cells and the fibre is not so clear as in the case of the cristae. Nevertheless, it can be definitely stated, that anastomosis or terminalretieulum never occur (Fig. 15). These two facts, especially the latter, must be emphasised as Racine described a terminalreticulum in the macula utrieuli of the cat

418 A..~brah~m :

providing herewith an anatomical base for that obsolete hypothesis and interpretation of the otologists according to which the vegetative nervous system also partly supplies the receptor apparatus of the labyrinthus with nerves. This has already been a much contested question since some time, the otologists being of the opinion that the autonomous nervous system is absolutely indispensable for the pathology and therapeutics of the labyrinthus and in correlation ~ith this the double innervation, this question has already previously been much discussed in connexion with the innervation of other receptor end-apparatuses. In this country 0DOSr POGAN'r M. D. enumerates in his book published last year many cogent physiological, pathological and clinical arguments in favour of the fact of the autonomic nervous system also participating in the nerve supply of the sensory zone of the labyrinthus. The trend of thought, observations and practical experiences of POG~X'r are undoubtedly logical and, especially considering the achieved treatment results perhaps even justified, nevertheless, the morphological structure which, on the base of RACI~E'S investigations he considered as decisive for the decision of such an important question is insufficient, the more so since RACINE's establishments are themselves not adequate. I{ACINE namely, as can be seen from Poo,iIgY'S book had already since a long while been seeking in the membraneous labyrinthus of the mammals for the fibres belonging to the autonomous nervous system. But it was not until 1942 that he reported a terminalreticulum of the macula acustica of the cat proving according to him his old supposition that besides the nerve fibres of the nervus acustieus, autonomic, respectively according to LANGLEY'S nomenclature para-sympathetic fibres also take part in the sensory nerve supply of the sensulae. ;RACISrE bases his statement on the single, exclusively morphological fact, of having found a terminalreticulum in the epithelium of the macula acustica of the cat. Unfortunately the author was not yet able to study RAClXE's preparations, however, of the drawing published in POG~NY'S book it can most certainly be stated that it is not a terminalreticulum. STOI~R, a BON~IA~ anatomist and neurologist was the first to describe on the base of preparations of one of his pupils REISSrE~ a terminalreticulum. These preparations wele prepared by BIELSCtIOWSKY'S method from the muscular layer of the human processus vermiformis. Later STOI~R also detected this form of nerve-ending in his own preparations, which according to him functions as accomplishing organ in the field of the autonomic nervous system, moreover SETO HAC~IIRO another of STOHR'S pupils has also described such kinds of formations in the human heart and walls of the blood vessels. According to STOgR'S determination this ternlinalreticulum is but a veil in which the most delicate nerve fibres are connected in the form of a net. The latter spreads over the ganglia and smooth muscle cells and nerves of


widely varying origin enter it. According to STSI~ this STSHR-I~EISER terminMreticulum would be the system, which on the One hand combines the cells of the autonomic nervous system into a powerful sincytium and on the other hand constitutes the plasmatic connexion between the accomplishing organ and the nervous system. These establishments of STSHR provoked a lengthy debate between the neurohistologists. Somelike ]~EIS~ER and SETO HACHmO accepted STSER'S theories, but others: NONII)EZ

ABRAtt~M, BOEKE and HART~NG tried in vain to find the terminalreticulum on preparations obtained f rom widely varying fields of the autonomic nervous system. BOEKE held the view of the terminalreticulum simply

being a reticular tissue. ABRAHXM was not able to detect this end-forma- tion on any kind of preparation, or under any kind of power magnification. He is therefore obliged to deny the occurrence of the terminah'eticulum. The author has already several times stated his opinion on this subject in communications published in Hungarian and German language, whereupon STSHR'S rejoinder was tha t in his opinion my neurohistological technic is not enough elective, as it might be that the terminalreticulum is only visible at a point where the nerve is no more visible to me. As this question could apparently not be solved in a reassuring manner by reciprocal a t tacks and replies, or by the best preparations at my disposal, the author travelled to Bonn in the summer of 1938 hoping to settle the question personally. In Bonn he was shown numerous very fine nerve preparations, many of which were placed under the microscope by STSHR himself, but in spite of this the author must honestly confess tha t his opinion has not changed, he still maintains his belief of the non-existence of the terminalreticulum. But assuming t h a t ~ a l t h o u g h so far it was not possible to detect them convincingly~after all such formations t ransmit the impulses in the field of the vegetative nervous system, it must yet be stated most decisively that what can be seen on RAcI~E's dra~4ng is not either according to the nomenclature of STSHR a terminalreticulum and it must be emphasised tha t in the macula acustica of the carp there is no terminalreticulum. Namely in the macula there is no anastomosis, neither among the nerve stumps nor among the branches, nor even among the quite thin, almost neurofibrillary end- branchings. And if there is no anastomosis there is no terminalretieulum. But even if there would be anastomosis and neurofibrfllary end-nets even these would not prove the fact of the nervous system of the sensulae also having autonomic fibres, as the only criterion of the autonomic origin of the fibres is the cell, respectively the ganglion, from which it derives.

The labyrinthus undoubtedly contains autonomic fibres, these are, however, only vasomotors associated to the blood vessels also insuring the life of the sensulae, however, in the epithelium where there are no

420 A..~brah~m :

blood vessels it has so far not been possible to denmnstrate them even by the best methods. Those branches and fibres providing the sensory elements of the cl~stae and maculae are all end-branches of the ramuli and at the extreme point the dendrites of the bipolar cells of the ganglions, not showing either in origin, or structure, or position any characteristics implying in any maturer their autonomous origin. Thus it must be stated

Fig. 16. Cyp~finus carpio L. Macula lagenae. Nerve plexus f rom the neuroepi tbel ium. BIE]SSCN0WSKY method , a ne rve f ibre , b neuroepi thel ium, c ne rve t e rmina t ion , d neurofibrlls . Microscopically 900 >~

magni f ied , photographical ly diminished to the 1/a.

that so far, there is no kind of morphological base supporting the interesting, and in many respects motivated assumptions, of RACINE, POGA~Y and othere.

After dealing with the macula acustica, disregarding the inaculae neglectae, decisively exhibiting in their structure and connexion with the ramulus neglectus similar conditions to the macula recessus utriculi, furthermore also neglecting the macula sacculi, the macula lagenae will be dealt with, the more so since the innervation of the small macula sacculi of the carp does not deserve particular attention. The macula lagenae, corresponding to the asteriscus, is a more extensive sensory epithelium surface being nearest from the histological point of view to


the generally known epithelium of the sensulae. The epithelium of the lagena is composed of more rows of cylindrical epithelial cells. The rounded off hair cells are well differentated, the sustentacular cells are less numerous, the nuclei of the lat ter are not so varyingly distributed, consequently their appearance of being manifold layers is not so striking. The nerve fibres enter the sensory epithelium from the ramus posterior the fibres of which conform in shape, distribution, arrangement and structure of the cells with those of the ramus anterior, the only possible difference being tha t the cells are still bigger and the fibres still thicker. As the macula is long and wide, the ramulus on the other hand pro: portionally thick, the nerve bundles entering through the apertures of the lamina propria ~re usually thinner, but the entering fibres themselves are also thinner and corresponding to the narrowness of the epithelium the terminal knobs of the nerves are also somewhat smaller, their rich branch system adjoins closely to the sustentacular and sensory cells (Fig. 16). For the rest the fibres entering the epithelium also exhibit the thickenings generally characteristic for the labyrinthus of the carp, the arborization is also abundant and as a consequence of the great distance between the entering bundles the pr imary branches run for a long distance in the middle of the epithelium, proceeding quite parallel to the surface of the latter, and in general the epithelium of the sensula is far thinner than tha t of the crista, or maculae of the utriculus. From these branches running longitudinally very fine fibres enter the base of the hair cells adjoining there to the plasma of the cells. The author has as yet not been able to detect on any hitherto prepared preparations nerve- endings, proceeding like in the crista, quite on the surface of the epithelium. This circumstance, but the entire nerve supply of the macula imphes that the sacculi is a less sensitive receptor organ then the crista. This circumstance may also mean tha t the labyrinthus has a larger share in the balancing, than in the transmitt ing of the waves which seems to be in accordance with its generally assumed physiological role.

Particularly for the sake of the elucidation of the role of the labyrinthus, taking the above cited facts into consideration, the author must draw the attention to yet another important area of investigation, which might perhaps also promote the question of the double innervation, i. e. to the origin of the nervus acusticus. This question will perhaps be dealt with later elsewhere. Namely from the so far pursued investigations it seems likely that the t ract of the acusticus also involves fibres originating in other brain nerves connecting the labyrinthus with the side-line organ, thus the possibility of fibres of autonomous origin entering the labyrinthus in this manner cannot be excluded, all the more since the question of the fibres of autonomous origin of the central par t of the head in general must still be ranged among the questions waiting for solution.

422 A. =~brahs :

Everything which the author has so far cited orally and exhibited in drawings concerning the connexions and finer structures of the labyrinthus and nervus acustieus of the carp is quite new to the literature. In this connexion of course it should be emphasised that the investigations are not quite concluded, and that besides some data which has still to be supplemented, the sinus superior in which the author has already observed nerve fibres, furthermore the maculae negleetae and the macula saeculi must still be studied. For this purpose the hitherto employed procedures will be undoubtedly suitable and the experiences gained at the above cited investigations very useful. The examination of all these questions is the task of the future and let us hope that on the base of the so far achieved anatomicM and histoteehnicM experiences it will be possible to solve them, if also not on the carp, perhaps on the head of some bigger sheatfish which at a time when the author was not yet in the position to deal with these questions used to be a fairly common prey of the fishers of Szeged. In mentioning this the author refers above all to the heads of those two sheat-fishes Which had a body weight of 100 kg. each, and are in the state of not completed preparations in his institute and to those other two shear-fishes weighing between 120-125 kg. which were also fished in the course of the last six or seven years in Szeged in the Tisza.

RETzIus asserts in a study on the hearing organ of the Perca Fluvia- tills: ,,Es liegt kein Grund vor, ein Auslaufen der Nervenfasern his zur Epitheloberflache anzunehmen." This conception is theoretically correct, however, nowadays the facts exhibit other evidence, namely according to the author's examinations in the crista of the carp the nerve fibres penetrate until the surface of the epithelium ending freely there. On the other hand, the fact described by certain investigators of the nerves also entering into the hair of the hair cells nmst be ranged into the realm of pure imagination. But also the report describing neurofibrils running in the hairs and nerve fibres in the tectoria lack all scientific base. All this is phantasmagoria originating in a super evaluation and unwarrented explanation of simple histological preparations of no value.

RETZlUS, having acquired great merits as nerve investigator and having indeed in general found in the animal realm and in many organs the existing connexions between the receptors and sensory organs, sin- eercly confesses regarding the innervation of the la.byrinthus of the bone fishes: ,,endgiiltig ist jedoch die Frage yon der schlieglichen Endigungs- weise der HSrnerven in den Cristae und Maculae acusticae beim Barsche wie bei den Knochenfischen fiberhaupt, nicht entschieden; dazu ist eine Pr/iparationsweise notwendig, wodurch sich die Endelemente des Nerven in sicherer Verbindung mit den Nervenfiiserchen darstellen lassen". Considering the above reported investigations the author believes beyond

The Endings of the Nervus Aeustieus in the Labyrinth of the Carp. 423

doubt to have found this ,,Pr~parationsweise" and thus to have succes- fully solved the question.

7. Summary.

I. The labyrinth of the carp is a membraneous labyrinth the rostral part of which is the utriculus with the semicircular canals, the caudal part, the saeculus and the lagena which is closely connected with the latter.

II . In the labyrinth, apart from smaller accessory and not constant :stones, there usually are three bigger otholiths one of them is in the utriculus, one in the sacculus and one in the lagena. In the recessus utriculi of the utriculus we find the ovoid, convex, concave lapillus, in the sacculus the long thin three-edged sagitta and in the lagena the big spheric, on one border incised, flat asteriseus.

I I I . The membraneous labyrinth is exclusively innervated by the nervus acusticus which divides after it leaves the medulla oblangata into two branches. One of them is the ramus anterior giving rise to three branches. These are the ramulus ampullae rostralis, ramulus ampullae lateralis and ramulus recessus utriculi. The other branch of the nervus acusticus is the ramus posterior, the branches of which are the ramulus sacculi, ramulus lagenae and ramulus ampullae caudalis. At the branching of the ramulus lagenae and ranmlus ampullae caudalis there runs still a small branch the ramulus neglectus.

IV. There are eight sensulae. Of these three are cristae and five maculae. The cristae are: the crista acustiea ampullae rostralis, the crista acustica ampullae ]ateralis and the crista acustica ampullae caudalis. The maculae are: the macula acustica recessus utriculi, the macula acustica sacculi, the macula acustica lagenae, and the two maculae acusticae neglectae.

V. The cristae acusticae are bodies bulging out from the wall of the ampullae, sinking deep into the lumen, bearing on the side of the lumen

relatively thick epithelial cap. This is really speaking the receptor organ. The fibres of the nervus acusticus end in this cap.

VI. The maculae are different sized bulges consisting of a neuroepithelium, proceeding gradually into the one layered cubic epithelium of the labyrinth.

VII . The epithelium of the cristae consists of several rows of cylindrical epithelial cells, the components of which are the hair cells of the surface and basicly situated sustentacular cells, the upper tapering section penetrateing into the hair cells.

VIII . On the base of the ramus anterior there is the longish flat ganglion vestibulare the cells of which are typical bipolar ceils exhibiting in a distinctness which can not be observed elsewhere the neurofibrils.

424 A. ,~brahs The Endings of the Nervus Aeusticus.

IX. The fibres running to the epithelium of the cfistae are strikingly thick, thickening to a still greater extent in the lower part of the epithelium, this thickening is especially conspicious at the point where the fibres begin their very abundant arborization. At this point the single fibres turn into stumps exceeding manifold the original diameter of the fibres. The place of these stumps appear to be, using the customary staining methods, columns tubes and lacunae.

X. The thick intraepithelial stumps begin to ramify in the median portion of the epithelium.

The arising branches are so nunmrous that the whole neuroepithelium appears indeed to be a real nerve tissue.

XI . A part of the end-fibres terminate under, and beside the hair cells in small fine end-knobs, the other part ending quite on the surface also in end-knobs.

XI I . The neuroepithelium of the maculae is also a cylindric epithelium composed of several rows. Most of the nerve fibres arising in the ramus posterior are also thick.

The delicate end-fibres arising from the abundant arborization of the former, end freely in the upper part of the neuroepithelium among the epithelial cells.

X I I I . In the neuroepithehum of the cristae and maculae there does not occur anastomosis among the nerve fibres, nor among the end-fibres, there is no terminalreticulunl and there are no parasympathet ic fibres. Thus as a consequence of these establishments RACINE'S anatomic base concerning the double innervation of the auditory organ has lost its value.

XIV. The macula lagenae corresponding to the asteriscus is a larger neuroepithelium area agreeing with the known sensula structure. The nerve fibres run from the ganglion of the ramus posterior which has a similar structure to that of the ganglion vestibulare. The nerve fibres proceed in bundles through the apertures of the lamina propria, thicken greatly in the epithelium, arborizing richly, their thin branches end freely, par t ly among the cells and part ly on the surface.

XV. As according to the above reported neurohistological examinations there are neither sympathet ic nor parasympathet ic fibres, nor a terminalreticulum in the neuroepithelium of the membraneous labyrinth, for the present we have no kind of morphological data affording anatomical proof for the double innervation of the auditory organ.

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The endings of the nervus acusticus in the labyrinth of the carp