On the physiology of the semicircular canals and their relation to seasickness

Front matter

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QP471 .B99 On the physiology of

Preface

Six years ago the author undertook to write an article on the etiology of seasickness. Not satisfied with a mere expression of views without appeal to experimental fact, and believing that the semicircular canals were in some way involved in the causation of the malady, he undertook of his own suggestion and forethought, a series of experiments using rotations, aural irrigations, stimulation of the retina by strong light, galvanism applied to the mastoid areas, etc., to determine whether by such means phenomena resembling those of seasickness could be experimentally reproduced. The results of his earliest experiments fulfilled his expectations to such an extent, that he proceeded to a thorough study of the semicircular canals, as affected by rotations, aural irrigations and galvanism.

The phenomena of nystagmus and the displacements of the head that occur in rotations, aural irrigations, and galvanism applied to the mastoid areas, were observed by him independently and the mechanisms involved in their production studied and worked out before he had any information of the work done by Barany, Neumann and others. He makes therefore, no pretensions for this part of his work on the score of priority in time, but submits it to the profession in the hope that the work will speak for itself.

Armed with the knowledge and experience gained from a thorough study of the sickness produced by rotations,

v vi PREFACE

aural irrigations, etc., he next proceeded to the experimental study of seasickness, the results of which are detailed in Part III.

Although numerous volumes were consulted the author owes special acknowledgment to the works of Ferrier, Sherrington, Piersol, Risien-Russell, and Ewald. The description of the labyrinth and of the eighth nerve is taken mainly from Piersol' s Human Anatomy.

The author wishes to thank Dr. Bailey and Messrs. William Wood & Co. for permission to reproduce three figures from Dr. Bailey's work on Histology. He also wishes to thank his friend Mr. Hugh J. Smith for the patience and fortitude with which he submitted to the various tests, as well as for the intelligent assistance given in describing the subjective phenomena.

The author has always been an acute sufferer from seasickness, and the time and labour devoted to these investigations, which were conducted in private, he considers well spent if his efforts tend to a better understanding of this distressing malady, with consequent alleviation of unspeakable human misery.

J. Byrne.

29 West 61st Street, New YorK City, January, 1912.

Part I General Anatomical And Physiological Considerations

CHAPTER PAGE

I. Anatomy of the Labyrinth 3

XL The Eighth Nerve . 12

III. The Remaining Cranial Nerves .... 22

IV. Blood-supply of the Labyrinth and of the

Cranial Nuclei 37

V. Synopsis op Anatomical Connections . . 40

VI. The Sympathetic or Autonomic Nervous

System 98

VII. The Paths Involved in Pupillary Movements 105

VIII. Further Anatomical and Physiological Considerations 114

Part II Physiology Of The Semicircular Canals

IX. Physiology of the Semicircular Canals FROM THE Standpoint of Animal Experimentation 125

X. The Effects of Passive Rotation . . . 130

vii viii CONTENTS

CHAPTER PAGE

XL The Effects of Rotation upon the Digestive

Apparatus 164

XII. The Effect of Drugs and Other Measures UPON Derangements of the Alimentary System Caused by Rotation Sickness . . 183

XIII. The Effect of Rotation upon Equilibrium 192

XIV. The Effects of Rotation upon the Eyes . 198

XV. The General Effects of Aural Irrigations 207

XVI. The Effects of Aural Irrigations upon the

Digestive Apparatus 233

XVII. The Effects of Aural Irrigations upon the

Eyes 250

XVIII. The Effects of the Galvanic Current upon

the Semicircular Canals 268

XIX. How Rotations, Aural Irrigations and Galvanism Affect the Labyrinthine Receptors and the Related Effectors . . .273

XX. Mechanism of the Nystagmus of Rotations,

Aural Irrigations and Galvanism . . . 288

XXI. Relations of the Semicircular Canals to the Oculo-Motor Nuclei and their Bearing UPON THE Results of Certain Experiments 306

XXIL On Ocular Movements and Nystagmus . . 315

XXIII. On the Occurrence of Nystagmus . . .331

Part III

XXIV. Studies in Seasickness 339

XXV. Further Studies in Seasickness During a

Transatlantic Trip 345

XXVI. Studies in Seasickness (Continued) . . .357

CONTENTS ix

PAGE

CHAPTER

XXVII. Studies in Seasickness (Continued) . . .379

XXVIII. Studies in Seasickness (Continued) . . .384

XXIX. General Conclusions from Studies in Seasickness. Protocols 417

XXX. History and Literature of Seasickness . 473

XXXI. Etiology of Seasickness 4S6

XXXII. Etiology of Seasickness (Continued) . . 496

XXXIII. On the Occurrence of Seasickness . . .508

XXXIV. The Effects of Seasickness and Their Re-

lation TO Diseased Conditions . . . .512

XXXV. How Recovery from Seasickness Takes

Place. Outlines of Treatment . . .518

Chapter I Anatomy Of The Labyrinth

The long axis of the internal ear measures about 20 mm, and corresponds with that of the petrous bone. The cavity of the bony labyrinth is divided into an anterior portion, the cochlea, a middle portion, the vestibule, and a posterior portion, the semicircular canals. The vestibule is an irregularly elliptical cavity measuring about 5 mm from before backward, the same from above downward, and about 3 — 4 mm from without inward. The outer wall constitutes that part of the inner wall of the tympanic cavity in which the oval window is situated. The medial or inner wall is directed toward the bottom of the internal auditory canal, and has two depressions separated by a ridge — ^the crista vestibuli, the upper pointed end of which forms the pyramidalis vestibuli. The anterior, the smaller of these depressions, is the spherical recess and lodges the saccule. In the lower part of this fossa a number of perforations (about a dozen) mark the macula cribosa media, through which pass, from the bottom of the internal auditory canal, the branches of the vestibular nerve to the saccule. The posterior, larger depression, is the elliptical recess, which lodges the utricle. Behind the lower part of the spherical recess the crista vestibuli divides into two limbs, between which is the recessus cochlear is, which lodges the beginning of the ductus cochlearis, and is pierced by a number of small openings for passage of the nerve filaments to this duct. The openings in the crista vestibuli and the elliptical recess collectively form the macula cribrosa superior, and transmit branches of the vestibular nerve to the utricle and to the ampullae of the superior and horizontal semicircular canals. Below and behind the recessus ellipticus lies a groove, the fossa sulciformis, which deepens pos-

4 SEMICIRCULAR CANALB

teriorly into a ven^ small canal — the aqugeductus vestibuli, and runs in a slightly curved course to the posterior surface of the petrous bone, where it ends in a slitlike opening — the apertura externa aqugeductus vestibuli, situated between the internal opening of the internal auditorycanal and the groove for the lateral sinus. The canal transmit-s the ductus endolymphaticus and a small vein. The anterior wall of the vestibule is pierced by the large opening leading into the scala vestibuli of the cochlea. Near this opening is seen the beginning of the lamina spiralis ossea, which lies on the floor of the vestibule below the oval window. Posteriorly the vestibule communicates with the semicircular canals by five small openings.

The semicircular canals are three small bony tubes, of a shape indicated by their name. They constitute the posterior division of the bony labyrinth. The direction of each canal corresponds roughly with one of the fundamental planes of the body, viz., the superior canal corresponds with the coronal or frontal, the posterior with the sagittal, and the horizontal with the transverse. The plane of their direction is such that each canal is at right angles to the direction of each of its fellows. At one end of each canal there is a dilated portion — the ampulla. The superior canal lies farthest front, and in nearly a vertical plane at right angles to the long axis of the petrous bone. The plane of the posterior, which is the longest of the canals, is approximately parallel to the long axis of the petrous bone. The external portion of the horizontal semicircular canal forms a prominence in the inner wall of the middle ear, behind the facial canal, while the upper part of the superior semicircular canal produces a conspicuous elevation — the eminentia arcuata, seen on the superior surface of the petrous bone. The canals open into the ]:)ost(3rior part of the vestibule by five openings, the undilated ends of the superior and posterior canals uniting U) form a common trunk, the crus commune. The iKjrizontal canal alone has two distinct openings into the vestibule. Its ampulla is at its outer end, and lir'H at the iippnr ))ait of the v(?stibule, above the oval window, from wliich it is sf^mrated by a groove corresponding with the facial canal.

The ampullary end of the posterior canal lies on the floor of the vestibule, near the opening of the undilated end of the horizontal canal and that of the canalis communis. The ampulla of the superior canal lies in the vicinity of the ampulla of the horizontal canal, but is situated somewhat mesial to it. This is an important relation in view of the fact that stimuli by means of irrigations in the external auditory canal, or by means of galvanism over the mastoid area, usually affect the ampulla of the horizontal canal only; but if thermic irritation be long continued, or if there be structural changes due to long-continued disease of the middle ear, pheno-

AmjpuUas

Ampulla

The Bony Labyrinth.

{From " Histology," by Dr. Bailey.

X3. (Heitzmann.)

Wm. Wood & Co., Publishers)

mena indicating irritation of the ampulla of the superior canal may appear simultaneously with those from irritation of the ampulla of the horizontal canal, or may even be present to the exclusion of the latter. In the wall of the ampulla of the posterior canal a number of small openings constituting the macula cribrosa inferior provide for entrance of the special branch of the vestibular nerve, destined for this canal. Sappey ^ states that the superior canal bends somewhat upon itself, so that the anterior (external) half inclines a little inward {e7i dedans), and the posterior (internal) half inclines a little outward (e7i deJiors). Poirier and Charpy^ follow Sappey 's description, which is undoubtedly accurate.

The membranous labyrinth lies within the bony labyrinth, and resembles it in general form. This agreement is least marked in the vestibule, since here the bony capsule is occupied by two compartments of the membranous sac — the utricle and saccule. The membranous labyrinth comprises :

1. The utricle and saccule, which, with the ductus endolymphaticus, lie within the vestibule.

2. The three membranous, semicircular canals, which lie within the bony canals.

3. The membranous cochlea enclosed within the bony cochlea.

The membranous labyrinth is attached especially at certain places by connective tissue to the inner wall of the bony capsule. The space between the membranous and bony labyrinths — largest in the scala tympani and scala vestibuli of the cochlea and in the vestibule — constitutes the spatium perilymphaticum, and contains a modified lymphatic fluid, the perilymph. The fluid which fills the interior of the membranous labyrinth is called the endol}mi23h, and can pass from one part of the labyrinth to another, although the saccule and utricle are only indirectly connected through a narrow channel — the ductus endolymphaticus. The utricle occupies the recessus ellii:)ticus in the uj^per and back part of the vestibule. Larger than the saccule, it communicates with the three membranous semicircular canals. It is attached to the upper and inner walls of the vestibule by connective tissue. It extends from the roof of the vestibule backward and downward to the opening of the j^osterior ampulla (5.5 to G mm).

The utricle has three subdivisions, the uppermost a blind sac (3 to 3.5 mm in length and breadth), called the recessus utriculi, whilst the two lower divisions form the utriculus proprius, which measures 8 mm by L 5 to 2 mm. The lower part of the utricle proper is prolonged into the tube-shaped sinus posterior, which connects the ampulla of posterior canal with the utricle.

The openings of the semicircular canals into the utricle are as follows : (a) Into the recessus utriculi : the ampulhe of the superior and horizontal canals, (b) Into the utriculus proprius :

ANATOMY T

1. The sinus superior, which lies within the crus commune, and receives in turn the non-ampullated ends of the superior and posterior canals.

2. The non-ampullated end of the horizontal canal.

8. The ampulla of the posterior canal through the sinus posterior.

On the antero-lateral wall of the recessus utriculi is placed the macula acustica of the utricle, whilst from its antero-mesial wall springs the canalis utriculo-saccularis, the small canal from the utricle that joins a still smaller passage from the saccule to form the ductus endolymphaticus.

The saccule is an irregularly oval compartment, about 8 by 2 mm, occupying the recessus sphsericus in the lower and anterior part of the vestibule, to w^hich it is attached by connective tissue. It is somewhat flattened laterally, and at its lower end gradually narrows into a passage — the canalis reuniens, which connects the saccule with the ductus cochlearis. Its upper end bulges backward, forming the sinus utricularis, the wall of which comes in contact with that of the utricle. The small canal that helps to form the ductus endolymphaticus springs from the posterior wall of the saccule. The ductus endol}miphaticus passes through the aquseductus vestibuli to end in a blind dilated extremity, the saccus endol}Txiphaticus, lying between the layers of the dura mater below the opening of the aqueduct. Through openings in the recessus sphsericus branches of the vestibular nerve enter and pass to the macula acustica sacculi on the anterior wall of the saccule. The canalis reuniens is the very small tube passing from the lower part of the saccule into the upper wall of the cochlear duct, near the caecum, as its blind vestibular end is called.

The membranous semicircular canals (ductus semicirculares) occupy about one-third of the diameter of the osseous canals, and correspond with them in number, name, and form. They are closely united along their convex margins with the bony tubes, whilst the opposite concave margins lie free in the perilymphatic space, being attached only by irregular vascular connective-tissue bundles (ligamenta labyrinthi canaliculorum) , which stretch across this space. Each of the membranous tubes has an ampulla, which is relatively much larger than the osseous ampulla, being three times the size of the rest of the tube. The part of the ampulla corresponding to the convexity of the semicircular canals is grooved on the

Diagram of the Perilymphatic and Endolymphatic Spaces of the Inner Ear. (Testut.) Endolymphatic spaces in grey; perilymphatic spaces in black. 1, Utricle ; 2, saccule ; 3, semicircular canals; 4, cochlear canal; 5, endolymphatic duct; 6, subdural endolymphatic sac; 7, canalis reuniens; 8, scala tympani ; 9, scala vestibuli ; 10, their union at the helicotrema; 11, aqueduct of the vestibule; 12, aqueduct of the cochlea; 13, periosteum ; 14, dura mater ; 15, stapes in fenestra ovalis ; 16, fenestra rotunda and secondary tympanic membrane.

{From "Histology," by Dr. Bailey. Wm. Wood & Co., Publishers)

outer surface at the entrance of the ampullary nerves. On the corresponding inner surface is a projection — the septum transvorsum — which practically divides this space inUj two parts, and is surmoimtod by the crista acustica, which contains the ampullary endings of the vestibular nerves. The crescent-shaped thickening beyond each end of the crista is called the planum semilunatum.

Structure of the Utricle^ Saccule^ and Semicircular

Canals.

The vestibule and the bony semicircular canals are lined by a very thin periosteum, composed of a feltwork of resistant fibrous tissue containing pigmented connective-tissue cells. Endothelium everj^where lines the perilymphatic space between the membranous and osseous canals, covering the free inner surface of the periosteum, the fibrous trabeculae, and the outer or peril}Tnphatic surface of this part of the membranous labyrinth. The walls of the utricle, saccule, and membranous semicircular canals are made up of (a) an outer fibrous connective-tissue lamella, and (b) an iimer epithelial lining, the latter consisting throughout the greater part, of its extent of a single layer of thin, flattened, polyhedi-al cells. Beneath the epithelium, in the region of the maculae and cristae, is (c) a thin, almost homogeneous, hyaline membrane with few cells. This middle layer presents, in places, on its inner surface small papillary elevations covered by epithelium. On the concave side of the semicircular canals is a strip — ^the raphe — of thickened epithelium, in which the cells become low, cylindrical in type. In the plana semilunata the cells are cylindrical in type. Over the regions receiving the nerve fibres — the maculae acusticse and the cristae acusticae — the epithelium undergoes a marked alteration, changing from the indifferent covering cells into the highly specialized neuro-epithelium.

The maculae acusticae are about 3 mm long by 2 mm broad, the macula of the saccule being a little narrower (1.5 to 1.6 mm) than that of the utricle (2 mm). At the margin of these areas the cells are at first cuboidal, next low columnar, and then they abruptly increase in length until they measure from 0.30 to 0.3o mm, in contrast with their usual height of from .003 to .004 mm. The acoustic area includes two kinds of elements — the sustentacular or fibre cells and the hair cells. The sustentacular cells are long, rather narrow, irregularly cylindrical elements, and extend the entire thickness of the epithelial layer, resting upon a well-developed basement membrane by their expanded or divided basal processes. At a variable distance from the base they present a swelling enclosing an oval nucleus, and terminate at the surface in a cuticular zone. The cylindrical hair cells are broader but shorter than the sustentacular cells, and reach from the free surface only as far as the middle of the epithelial layer, where each cell terminates usually in a rounded or somewhat swollen end, containing a spherical nucleus. The end next to the free surface exhibits a differentiation into a cuticular zone, similar to that covering the inner ends of the sustentacular elements.

From the free border of each hair cell a stiff, robust hair, .020 to .025 mm long, projects into the endolymph. This, however, is resolvable into a number of agglutinated, finer hairs or rods. The free surface of the neuro-epithelium within the saccule and utricle is covered by a remarkable structure, the so-called otolithic membrane. This consists of a gelatinous membrane, in which are imbedded numberless small, crystalline bodies, the otoliths. Between it and the cuticular zone is a space, about .020 mm in width and filled with endolymph, through which the hair cells pass to the otolithic membrane. The otoliths are minute crystals, usually hexagonal in form, with slightly rounded angles, and from .009 to .011 mm in length. They are composed of calcium carbonate, with an orgjinic basis. On reaching the macula the nerve fibres form a subepithelial plexus, from which fine bundles of fibres pass toward the free surface. The fibres usually lose their medullary substance in passing through the basement membrane, and enter the epithelium as naked axis-cylinders. Passing between the subcuticular cells to about the middle of the epithelium, they break up into fine fibrilla), which embrace the deeper ends of the hair cells, and give off fine threads tliat pass as free axis cylinders between the cells to higher levels.

The crista acustica and planum soinilimatum are covered with neuro-epitheli urn, similar to thatof the macula). The hairs of the hair cells, however, are longer and converge to, and are imbedded witliin, a peculiar domelike structure known as the cupola, regarded by some anatomists as an artefact formed by coagulation of the fluid

' ANATOMY I 11

in which the hair cells are bathed. Otoliths probably do not exist in the cristse acusticse.

In some lower animals, besides the maculae of the utricle and saccule, there is also a third structure similar to these — the lagena — which likewise contains otoliths. In certain fishes the otoliths are stones of 1 cm in size. The plane of the macula utriculi corresponds roughly with that of the external semicircular canal. In the uj)right position it is inclined backward at an angle of 45°. According to Ketzius 3 the long axis of the macula utriculi in men is directed from in front upward and inward and (the short axis) backward, downward, and outward, the general plane being about horizontal. The long axis of the saccule is almost vertical, and is directed from without upward and inward, the short axis being directed from before backward. The macula is situated upon its mesial surface (Retzius). The plane of the macula sacculi runs from above and behind forward and downward in an antero-posterior direction, at about an angle of 45°. The lagena of lower animals permits vertical displacement of its otolith, while the maculae of the utricle and saccule are roughly horizontal, and at right angles to each other (Piersol*). The hairs of the maculae of the utricle and saccule are stiffer and shorter than those of the cristae of the ampullae, and are held together by a stiffer mass of otoconium, which, however, is not gelatinous, but of otolithic composition. Yerworn ^ proposed the name staloliths for the otoliths of the utricle and saccule, and called the analogous organs in certain lower forms statocysts, thus assuming that the function of these organs is exclusively static, as distinguished from the dynamic function of the semicircular canals. Clarke,^ after a comparative study of the otolithic and related structures, concludes that whilst the otolithic structures are mainly statical in function, they are not exclusively so, and may function dynamically as well. With the exception of the maculae of the utricle and saccule no part of the vestibular wall is supplied with nerve terminals of the eighth nerve,

Chapter II The Eighth Nerve

The eighth nerve consists of two portions — the cochlear, or true nerve of hearing, and the vestibular, which is concerned with equilibration. Traced from the brain toward the ear, the eighth nerve arises at its superficial origin by two roots : a mesial — radix vestibularis — and a lateral — radix cochlearis — which embrace the inferior cerebellar peduncle, the mesial root passing to the inner, and the lateral root to the outer side of the peduncle. The nerve thus formed by the union of these two roots leaves the surface of the brain-stem at the posterior border of the pons, where it is adherent to the middle cerebellar peduncle. To its inner side, and closely associated with it, are the motor and sensory roots of the facial nerve, which lie within a groove on the mesial surface of the eighth, and with it enter and traverse the internal auditory canal. Within the latter the eighth nerve separates into two divisions, of which the superior and larger is the vestibular nerve (n. vestibuli), and the inferior and smaller the cochlear (n. cochleae). Although in a general way these divisions continue the corresponding roots, this agreement as to the source of their fibres is not complete, since strands of the vestibular fibres are incorporated with the cochlear nerve. On reaching the bottom of the internal auditory canal, the facial nerve enters the facial canal, whilst the fibres of the eighth nerve disappear through apertures in the lamina cribrosa, to reach the several parts of the membranous labyrinth. In the internal auditory canal the vestibular and facial trunks are connected (fila anastomica) by a branch, which passes from the pars intermedia to the vestibular nerve, and by one from the latter to the geniculate ganglion. These apparent communications between the seventh and eighth nerves are, in fact, only aberrant strands of facial fibres that return to the seventh after temporary association with the eighth.

The vestibular nerve divides into three terminal branches, which pass through the apertures in the cribriform plate, above the falciform crest, and supply the utricle and the superior and external semicircular canals. Not all the fibres of the vestibular root, however, are included in these branches, since of the three branches given off by the vestibular nerve, two, viz., those of the saccule and posterior semicircular canal, are incorporated v/ith the cochlear fibres, and seemingly are derived from the cochlear nerve. The remaining branch of the cochlear nerve contains the cochlear fibres proper, which traverse the numerous foramina of the tractus spiralis foraminosus and the central canal of the modiolus, to supj^ly the organ of Corti.

The fibres of the eighth nerve are afferent. Hence they are processes (axones) of nerve cells, situated somewhere along the course of the nerve. The real origin of the nerve fibres, therefore, is to be sought in the ganglia, occurring in the divisions of the nerve.

The true cochlear fibres arise within the cochlea as axones of the cells of the spiral ganglion, or ganglion of Corti (g. spirale). This structure consists of a series of bipolar neurones, which occupies the spiral canal in the base of the lamina spiralis. The dendritic processes of these cells begin as fine fibrils, which lie in close relation with the neuro-epithelial cells, comprising the inner and outer hair cells of the organ of Corti. Leaving the hair cells as non-medullated fibres, they traverse the foramina nervosa of the labium tympanicum, at which point they become medullated when they interlace to form a flat feltworkthat lies between the layers of the lamina spiralis, and soon assemble to form bundles which pass to the cells of the ganglion spirale, each fibre probably joining its individual cell. Leaving the ganglion, the axones of its cells enter the bony canals within the modiolus, from which they emerge as the tractus spiralis foraminosus, and are collected into a single bundle — the cochlear nerve proper. This latter, however, soon receives two accessions, one of which consists of fibres from the saccule, the other from the posterior semicircular canal. These accessions are in reality parts of the vestibular nerve and, beyond their temporary companionship have nothing to do with the cochlear root.

On reaching the medulla the cochlear fibres come into relation with their nucleus of reception, which includes two superficial aggi-egations of nerve cells that collectively constitute the acoustic nucleus. The latter consists of two parts, of which one — the ventral cochlear nucleus, also called the accessory acoustic nucleus — lies ventral to the inferior cerebellar peduncle ; and the other — the lateral cochlear nucleus, or tuberculum acusticum, rests upon the dorso-lateral surface of the peduncle, and occupies the extreme outer part of the triangular acoustic area, seen in the lateral angle of the floor of the fourth ventricle. The greater number of cochlear fibres end in arborizations around the stellate cells of the ventral ganglion, whilst others terminate in relation with the more elongated fusiform cells of the lateral nucleus. From the neurones of these subdivisions of the reception nucleus, the auditory pathway is continued as two chief tracts — the axones of the cells of the ventral nucleus passing for the most part ventral to the restiform body and the special root of the trigeminus to form the corpus trapezoides, whilst those from the lateral nucleus sweep around the outer surface of the restiform body, and then medially beneath the ependyma of the floor of the fourth ventricle, where they show with varying degrees of distinctness as the striae acusticse. The corpus trapezoides — the conspicuous transverse tract that separates the tegmental from the ventral region of the pons in its superior part — is formed chiefly by the axones of the cells within tlie central cochlear nucleus, supplemented by a limited number of fibres that spring from the lateral nucleus. In addition it contains axones from the large cells found within the trapezoid body on each side of the middle line that constitute the nucleus trapezoideus. In close relation with the dorsal surface of the corpus trapezoides, within the superior olive and on either side of the median raphe, lies the superior olivary nucleus (nuc. olivarius superior) , a collection of nerve cells around which many of the cochlear fibres, chiefly from the opposite but also from the same side, end and from which the tract of the lateral fillet principally takes origin. Not all the fibres arising from the superior olivary nucleus, however, enter the lateral fillet. A considerable number leave the dorsal surface of the nucleus, and as its peduncle pass to the abducent nucleus (v. Bechterew considers these fibres as cerebello-fugal paths to the abducens nucleus) , and by way of the posterior longitudinal fasciculus to the nuclei of the other ocular nerves. In this manner it is asserted the reflex paths are established, by which the motor nerves, including probably the facial, are brought under the influence of auditory impulses.

There are reasons, however, for rejecting this simple, almost direct relation between the eighth nerve and the nuclei of the eye muscles. Movements of the eyes in response to a loud sound are not simple reflex movements, but complex, coordinated movements, associated usually with other movements, e.g., turning of the head and eyes to the source of the sound, accompanied by a general movement of withdrawal of the head and upper part of the body. Such complex purposive movements could hardly take j)lace through direct paths from the auditory to the ocular and other nuclei without the intervention of some higher harmonising mechanism. Moreover, in Ferrier's^ experiments, stimulation of the auditory area in the temporal lobe caused the animal to turn the head and eyes in the direction of the ear of the opposite side. This interesting experiment shov»"s that the main relation between the auditory nerve proper and the cerebral cortex is a crossed one. It also shows that reflex, coordinated turning of the head and eyes in response to auditory stimuli may take place along other ]3aths than the direct one mentioned; that is, in a downward course, possibly through the medium of the cerebellum.