the protection of the laryngeal airway during swallowing

VOL. XXV, No. 296

THE PROTECTION OF THE LARYNGEAL AIRWAYDURING SWALLOWING

By G. M. ARDRAN, M.D., D.M.R., and F. H. KEMP, M.B., Ch.B., M.R.C.P., D.M.R.

From the Nuffield Institute for Medical Research, University of Oxford

INTRODUCTION

A MONG the first to use X rays to investigate* * the act of swallowing were the late Sir ArthurHurst of Guy's Hospital and Dr. A. E. Barclay, ofManchester. Barclay's studies, begun in Manchester,were continued in Cambridge and published in hisbook The Digestive Tract (1933). He recognised thatwhile it is easy to demonstrate the act of swallowingwith the fluorescent screen, it is extremely difficultto analyse certain phases of the movement as theytake place too quickly for the eye to follow. When hecame to Oxford he used kineradiographic apparatusfor this purpose, but was never satisfied with theresults obtained. Some of his 16 mm. films, takenat the rate of 16 frames per second, are still in theNuffield Institute.

Janker in Bonn, Ramsey in Rochester, N.Y., andReynolds in London, also used indirect kineradio-graphy, to demonstrate the act of swallowing. Nodetailed account of their observations has beenpublished. Frenckner (1949) published a descrip-tion by Holmgren of 16 mm. films taken at the rate of16 frames per second, but it appears that the detailobtained was not good enough to show what hap-pened when movement occurs quickly.

The authors have already given a general accountof the mechanism of swallowing elsewhere (Ardranand Kemp, 1951). The present paper is concernedwith the way in which the laryngeal airway is pro-tected during swallowing.

The time-honoured theory that the epiglottisturns down over the larynx to prevent food enteringthe airway has been questioned, since it has beenshown that the tongue of the epiglottis can be re-moved without apparent ill effects (Magendie, 1823),and it is now held that the epiglottis serves littleuseful purpose (Negus, 1949). Closure of the larynxis attributed to strong elevation against the base ofthe tongue. The thyro-arytenoid, lateral crico-arytenoid and inter-arytenoid muscles are believedto assist the closure of the superior laryngeal aper-ture.

Our kineradiographic studies have shown thatthese views are not entirely correct. We have found

that many safeguards exist to prevent food fromentering the lower air passages.

MATERIAL

About 500 examinations have been made ofswallowing in normal young European adults, ofboth sexes, under 30 years of age. Observations weremade of swallowing varying consistencies andquantities of barium emulsion. Kineradiographicfilms were taken at a speed of 25 frames per secondon 35 mm. film with apparatus which has been des-cribed by Ardran and Tuckey (1951-2).

RESULTS

General considerationsThe larynx begins to rise as the bolus* descends

upon the back of the tongue; and as the thyroidcartilage comes towards the body of the hyoid, theepiglottis is pushed posteriorly against the posteriorpharyngeal wall (Fig. la) and the bolus is receivedinto the valleculae (Fig. lb). Here there is a moment-ary pause; a little of the barium spills over the lateralpharyngo-epiglottic folds into the lateral foodchannels but the bulk of the bolus is held upon theepiglottis (Figs, lb, lc, 7). At this stage the vesti-bule of the larynx is usually open and in communica-tion with air in the hypopharynx* (Fig. lc).

When a sufficient quantity of barium has enteredthe mesopharynx-j- the larynx moves forward so thatthe tongue of the epiglottis comes away from thepharyngeal wall, allowing the bolus to pass (Fig. Id).The bulk of the bolus then passes down on one or

* We have used this word to mean (1) a rounded mass offood or fluid formed on the dorsum of the tongue in prepara-tion for swallowing and (2) as a term to describe that whichis swallowed. After leaving the mouth the bolus becomeselongated and sometimes may be said to have a head, bodyand a tail.

t We have found difficulty in employing the conventionalnomenclature for the divisions of the pharynx. The pharynxis divided into three chambers, an upper, middle and lower,by the soft palate and the epiglottis. The upper chamber orepipharynx is that part of the pharynx above the soft palate.The middle chamber or mesopharynx extends from thelower surface of the soft palate to the valleculae. The lowerchamber or hypopharynx extends from the valleculae to themouth of the oesophagus. The boundaries of these chambersvary according to the positions of the soft palate and theepiglottis.

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The Protection of the Laryngeal Airway during Swallowing

both sides of the larynx (Fig. 2) and only a little and varies between individuals. If retraction of thespills directly over the laryngeal entrance. The larynx forward is very pronounced, the epiglottisextent to which the larynx moves forward depends may stand out in the channel beneath the bolus "likeupon the size and consistency of the bolus swallowed a rock under a waterfall".

FIG. 1.

Selected prints taken from a film of a normal individual swallowing a mouthful of barium emulsion. Lateral projection.

(a) 5th frameThe larynx slightly raised and arched backwards. The epiglottis touching the posterior pharyngeal wall. The bolus descend-

ing upon the dorsum of the tongue.

(b) 1th frame"Vallecular arrest." The barium held on the epiglottis. A trace has passed into the lateral food channels.(c) 8th frameFurther elevation and arching of the larynx. Narrowing of the lumen of the vestibule of the larynx; most pronounced at

the entrance. Barium has passed into the lateral food channels.

(d) Wth frameThe lumen of the larynx is obliterated. The epiglottis is withdrawn from the posterior pharyngeal wall and is projecting

into the stream.

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G. M. Ardran and F. H. Kemp

As the larynx is raised and moved forward, thelumen of the vestibule is reduced to a narrow

(a) A still radiograph showing the valleculae and the lateralfood channels outlined by barium and partially distended

with air.

channel 2-3 mm. in diameter; at this stage, thelumen is usually arched backward. When the larynxis well arched, the epiglottis is bent to form a cowl-like hood above the laryngeal entrance, the sides ofthe hood serving to direct the bolus away from themidline into the lateral food channels (Figs. 2a,2d). The laryngeal entrance is well covered by theoverhanging epiglottis and sometimes further pro-tection is offered by air trapped beneath the epi-glottis. The arching of the larynx tips the vallecularcontents backwards.

The bolus descending the lateral food channels ischecked momentarily before it enters the oesophagusand sometimes builds up in the hypopharynxaround the larynx.

The larynx continues to be drawn upwards as thebolus is squeezed downwards. When the bolus haspassed through the mesopharynx forward retractionof the larynx ceases. Then as the dorsum of thetongue arches backward and the larynx moves back-ward, the tongue of the epiglottis is carried down-ward with the bolus as though it were being swal-lowed (Fig. 4). At this stage the larynx is archednearly 90° backward and the tip of the epiglottis isheld in the region of the mouth of the oesophagus

FIG. 2.The lateral food channels. Antero-posterior projections.

(b), (c) and (d) Three consecutive frames showing barium passing on either side of the larynx down the lateral foodchannels.

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(Figs. 4d, 4e, 4f). The lumen of the larynx, thoughconstricted, may still be patent, and it has fre-quently been observed that a column of air is drawnfrom the larynx and swallowed with the bolus. Asthe bolus is squeezed out of the lower pharynx alltraces of air and barium are expressed from thelaryngeal vestibule and from beneath the down-turned epiglottis (Figs. 3b, 3c), the lumen of the

FIG. 3.

Barium spilling into the laryngeal vestibule.(a) The subject swallowing a small fluid bolus. The larynxhas not been arched backwards. The epiglottis rests againstthe posterior pharyngeal wall. Barium has spilled into thevestibule—in this case passing into the laryngeal ventricle.(b) The vestibule of the larynx has commenced to contractfrom below and has squeezed some of the contents upwards.(c) The vestibule is closed except at the superior orifice.

Tzvo frames taken from the films of another individual.(d) Vallecular arrest. Barium has spilled into the lateral

food channels.(e) Barium has filled the lateral food channels and spilled

into the entrance to the vestibule.

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vestibule being obliterated from below upward. Asmall residue of barium remains on the upper sur-face of the epiglottis (Fig. 4h). The tip of the epi-glottis is ultimately folded forwards under thearched larynx (Fig. 4e), a position which it holdsuntil the airway has been re-established, or untilanother bolus is swallowed. The larynx remainsclosed while the bolus is passing through the crico-pharyngeal sphincter into the upper oesophagus.Then relaxation takes place from above and below;the larynx fills with air from below (Figs. 5a, 5b, 5c)as it returns to its normal position of rest and thepharynx fills with air from above. The epiglottissweeps upward to the erect position as the larynxfalls (Figs. 4f, 4g), and carries with it the residue ofbarium remaining on its upper surface. When theairway has been restored the subject resumes normalrespiratory movement.

VariationsThe above account represents the usual sequence

of events. There may be modifications dependingupon the behaviour of the individual and the sizeand consistency of the bolus swallowed. Thoughthere may be variations in timing and the degree towhich the different responses are made, the basicpattern of the swallowing movement is always thesame.

The modifications which take place in response tovariations in the size and consistency of the bolusswallowed are briefly as follows: when fluids arepassing, the superior aperture of the larynx andlumen of the vestibule are reduced to a narrowchannel, whereas when thick pastes are swallowedthe lumen of the vestibule may be relatively wideopen. In this region fluids are swallowed morequickly than pastes. Swallowing a small bolus usuallyresults in a smaller degree of closure of the vestibuleand less arching of the larynx than occurs whenswallowing a large bolus. Fluid is more apt thanpaste to spill into the laryngeal vestibule. The effectsof taste and temperature have not been considered.

The entry of food into the larynxA spill of food into the laryngeal vestibule takes

place frequently in nearly every normal individual.It is most apt to occur with the first mouthful. Thespill penetrates to a varying depth into the vestibule,often reaching the false cords, but seldom goingbeyond. We have twice seen barium enter the laryn-geal ventricle (Fig. 3a), but in normal individuals we

have never seen it penetrate the glottis. The totalamount entering the larynx is always very small, andis conditioned by the reduced size of the vestibularlumen. The commonest mode of spill usually occursearly in swallowing, immediately after the stage ofvallecular arrest, just as the epiglottis is being with-drawn from the posterior pharyngeal wall; at thisstage it is very liable to occur if the larynx has notbeen arched backwards sufficiently (Fig. 3a) andespecially if the amount being swallowed is small.

A spill may also be observed to result by fluidspreading over the moist undersurface of the epi-glottis into the vestibule. This kind of spill may takeplace even when the larynx has been well arched.

A third mode of laryngeal spill may occur afraction of a second later in the swallowing act. Thisis because a transverse furrow is produced in thehypopharynx by the forward retraction of the aryte-noids upon the cricoid cartilage. A small column ofbarium may be seen to pass along this furrow fromone or both lateral food channels towards theentrance to the larynx and may enter the vestibule.

A fourth mode of spill occurs as a result of thearrest of the bolus in the lateral food channels and isdue to the building up of a column of food in thehypopharynx; when the column reaches the level ofthe laryngeal orifice a spill may occur (Figs. 3d, 3e).

We have already explained that any trace of foodwhich enters the larynx is later expelled into thepharynx when the last of the bolus is being expressedinto the oesophagus; the lumen of the vestibule isobliterated from below upwards (Figs. 3b, 3c).

Our clinical observations suggest that certainpowders such as ginger, and oils such as cod liver oil,are apt to enter the larynx and excite coughing afterswallowing. We have not been able to confirm thisobservation radiographically, since it is extremelydifficult to reproduce the necessary conditions at thetime of taking the picture.

The closure of the larynxThe lumen of the vestibule may be entirely

obliterated without the larynx being raised. Closuremay occur before swallowing has started, or at anytime during the act. Confirmation of this finding hasbeen obtained from a study of the behaviour of thelarynx during breathing (Ardran, Kemp and Manen).It has been found that the lumen of the vestibulemay be closed without elevation of the larynx whenrespiratory movements are suddenly arrested (Fig. 6).

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FIG. 4.A series of selected prints of a volunteer who had a small silver clip fixed to the tip of the epiglottis.

Figs, (a), (b), (c), (d), (e), (f) and (g) show the movement of the epiglottis while swallowing a mouthful of water.

(a) The larynx at rest before swallowing commenced. The epiglottis iserect.

(b) 1th frame. After the commencement of swallowing. The larynx archedbackwards. The lumen of the vestibule narrowed. The epiglottis tipped

backwards against the posterior pharyngeal wall.(c) \9th frame. The lumen of the larynx obliterated. The epiglottis isturning down. The two images of the clip indicate the distance travelled

during the exposure.(d) 20th frame. Invertion of the tongue of the epiglottis now complete.(e) 25th frame. The tip of the epiglottis has moved forwards under the

arytenoids.

(f) 2%th frame. Reinflation of the airways commencing. The epiglottis,which is still turned down, is outlined between air in the pharynx above

and air in the larynx below.(g) 21th frame. The larynx is falling. Two images of the clip can beseen as the epiglottis sweeps upwards. At the 29th frame the epiglottis

had returned to its position of rest.(h) A single frame taken from another film of the same individual, afterswallowing a mouthful of barium. The arrow indicates the clip on thetip of the down-turned epiglottis. A residue of barium is seen on the baseof the epiglottis which would have been deposited over the mouth of thelarynx if the epiglottis had not been present. Compare with Fig. 8 (d).

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Swallowing via the lateral food channelsIt has been shown (Negus, 1949) that many lower

animals are provided with an efficient mechanismwhereby fluid is able to pass on either side of thelarynx without the danger of overflow into the air-way. The existence of this mechanism in man isaccepted, but many authorities believe that it is onlyused to transmit small quantities of fluid. We havemade many experiments in young adults with vary-ing consistencies of barium paste and with variousadded foodstuffs. In every case the bulk of thematerial has always been diverted into one or bothof the lateral food channels (Fig. 2). It has alreadybeen stated that in most cases some food passeddirectly over the larynx, but this is only a smallfraction of the total swallowed (Fig. 2d).

The behaviour of the epiglottisWe have found that during swallowing the tongue

of the epiglottis turns down. This action takes placelate in the act of swallowing, after the bulk of thebolus has passed. Confirmation that the movementof the epiglottis is independent of gravity has beenobtained by taking films in the erect and supinepositions and with the subject suspended upsidedown. Further proof was given by an experiment inwhich our colleague, Mr. Ronald Macbeth, placed asilver clip upon the tip of the epiglottis of a volun-teer. No form of anaesthesia was used and thesubject was examined swallowing water and bariumemulsion (Kemp, 1950). From the cinematographicrecords obtained it was easy to follow the movementsof the clip (Fig. 4). The speed of movement wascalculated at times to be of the order of 1 cm./20milliseconds, which explains why previous observershave encountered difficulty in obtaining satisfactoryrecords.

FIG. 5.Reinflation of the larynx from below. Three consecutive frames.(a) Complete obliteration of the lumen of the larynx and

pharynx following swallowing.(b) Reinflation of the airways has commenced. Thelaryngeal ventricle and the vestibule have filled with airfrom below. No air has entered the airway from above.(c) Further relaxation. Air has now passed from the vesti-bule into the pharynx. The epiglottis is seen outlined

between air above and below.Note—Reinflation of the larynx from below is usually

closely associated in timing with the entry of air into thepharynx from above, but in some instances, one mode of airentry preceded the other. The larynx always inflates frombelow.

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Through the kindness of Mr. F. Capps of St.Bartholomew's Hospital, we have had an oppor-tunity of examining one person from whom thetongue of the epiglottis had been removed. Some

FIG. 6.Two still radiographs showing complete closure of thelarynx with little elevation and without backward tilt.

(a) The airways in quiet respiration.(b) During sudden arrest of respiration. The hyoid bonehas not moved. These two films demonstrate the vestibular

sphincteric mechanism.

three years earlier this patient had had the tongue ofhis epiglottis removed for chronic ulceration. Hislarynx was otherwise normal. He stated that sincethe operation he had experienced no ill effects, but

that his wife complained that he ate his meals veryslowly. Kineradiographic examination of this patientshowed that, on swallowing barium emulsion,closure of the larynx was effected immediately thebolus left the mouth (Fig. 8b); there was no arrestin the vallecula and deviation of the fluid down thelateral food channels occurred at a slightly lowerlevel than usual. There was considerable delay in re-establishing the airway after the bolus had enteredthe oesophagus, which appeared to be due to thedeposition of barium upon the closed superioraperture of the larynx (Fig. 8d). The subject wasseen to make repeated attempts to open the airwayeither from below or from above, each attempt being

FIG. 7.The epiglottis acting as a true cover valve. The lumen of thelarynx is not arched backwards and is wide open. We haveonly seen the epiglottis acting in this manner twice in over

500 records.

followed by another swallowing movement. Ulti-mately the residue was removed and the airway re-established. The patient was not conscious of anydifficulty, but each complete act of swallowing tookat least five times as long as the normal, the delaybeing mostly due to the difficulty of re-establishingthe airway and not to the act of swallowing itself.Closure of the larynx was performed satisfactorilyand no spill of barium into the vestibule occurred.Protection was accomplished by instantaneousclosure of the vestibule by the muscular sphincterbefore elevation had occurred. Unlike the normalindividual complete closure was maintained through-out swallowing. On swallowing thick paste theurgency for closure of the larynx was not sogreat, but closure did occur whenever the bariumapproached the laryngeal aperture.

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DISCUSSION

The closure of the larynxIn 1892, Stuart, an Australian physiologist,

investigated the mechanism of closure of the larynxduring swallowing by observing the behaviour of aman who had had a large part of the side wall of his

and posteriorly by the apposed artenoids and theary-epiglottic folds. Similar appearances wereobserved when the subject was asked to makeexpulsive efforts. Two Melbourne laryngologistsconfirmed these findings. Stuart also operated on anumber of species of animals and found that they

FIG. 8.A series of frames from a patient who had the tongue of the epiglottis removed.

(a) Barium held in the mouth. The laryngeal airway is wide open. The tongue of the epiglottis has been excised near its base,(b) Swallowing has commenced. The lumen of the vestibule is considerably narrowed but not arched backwards.

(c) The descent of the bolus through the pharynx. Barium fills the mouth of the closed larynx.(d) The bolus has passed. The airway has not reinflated. A residue of barium lies over the mouth of the larynx. Compare

with Fig. 4h.

pharynx removed for carcinoma. He found that theentrance to the larynx is reduced to a T-shapedfissure. He stated that the vertical limb of thisfissure, which is the shorter, is formed by appositionof the arytenoids; the transverse limb, which is con-vex forwards, is formed anteriorly by the epiglottis

too behaved in a similar manner. He explained themechanism in the following words. "If, however, theentrance is to be closed as a part of the act ofswallowing, then of course, the well-known move-ment of the entire larynx upwards and forwardsensues, and the tips of the arytenoids are seen to be

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jammed firmly against the epiglottis. This is duepartly to the thyro-arytenoid vigorously rotating thearytenoids inwards and pulling them downwardsand forwards, so that their tips come into contactwith the base of the epiglottis; partly, however, it isdue to the elevators of the larynx pulling the larynxupwards and forwards against the base of thetongue."

Negus (1949) described the action of the intrinsicmuscles in bringing about closure of the superiorlaryngeal aperture, and Keene and Whillis (1950)considered that these muscles constitute a superiorlaryngeal sphincter.

Very little is known of the changes which takeplace in the interior of the larynx during deglutition.Many text-books contain a diagram showing thelarynx closed at the superior laryngeal aperture andthe lumen opened below. It has always been con-sidered that it is essential to keep food out of thevestibule on the grounds that the vestibule isextremely sensitive to mechanical irritation.

How is the vestibule controlled? The theory thatthe larynx is closed during normal swallowingentirely by its own strong elevation against the backof the tongue has not been substantiated. We haveshown that the lumen of the vestibule can beentirely obliterated without the larynx being raised,indicating that the vestibule must be controlled by asphincteric girdle of muscle. This sphincter con-tracts from below upward; relaxation also takes placefrom below upward.

The elevation of the larynx undoubtedly resultsin the lumen being narrowed and arched backward,and also results in a relative narrowing of the superiorlaryngeal aperture (Fig. lc). Closure of the larynxby other means is thereby facilitated. The retractionof the larynx forward in order to allow the bolus topass from the mesopharynx also helps to close thevestibule. If the larynx moves forward a great deal,as when an individual swallows a large bolus, or amass of thick paste, the lumen of the vestibuleusually closes and opens again as soon as the forwardmovement ceases.

We can only deduce what is happening to thelumen at the level of the false and true vocal cordssince we cannot clearly see the lumen at these levelsin all phases of swallowing. Obliteration of the lu-men of the vestibule is always associated withobliteration of the laryngeal ventricle; both true andfalse cords are probably closed at this stage. We infer

that the false cords are closed when we see that theyprevent entry of barium into the laryngeal ventricle.During entry of barium into the vestibule the trueand false cords may be open. Presumably both trueand false cords must be open when air is aspiratedfrom the larynx in the final phase of swallowing.Whether the false cords can ever close the larynxduring swallowing without closure of the vestibulewe do not know.

The function of the epiglottisWe have mentioned that it is considered that the

tongue of the epiglottis can be removed withoutapparent ill effects (Magendie, 1823). The truth orotherwise of this assertion is difficult to prove. Wehave been unable to trace any detailed account ofobservations on the behaviour of a patient fromwhom the epiglottis has been removed. Enquiriesamong laryngologists reveal that disease processessolely confined to the tongue of the epiglottis areseldom seen and operations for the removal of thetongue of the epiglottis alone are rarely performed.

Stuart and McCormick (1892) stated, from theirobservations on a patient with a pharyngostomystoma, that the epiglottis remained upright onswallowing. Barclay (1933-36) stated that when abolus of barium was swallowed the epiglottis wasfirst pushed backward against the posterior pharyn-geal wall and then retracted forward so that itprojected like a "rock under a waterfall". He wasunable to see what happened after the bolus hadpassed, but concluded that the epiglottis did notplay any vital part in the act of swallowing or inclosing off the larynx. Negus (1949) came to thesame conclusion from anatomical and clinical studies.

On the other hand, Moscher (1927), who madeseveral radiographic studies of deglutition, statedthat the epiglottis turned down. Hegner (1936) cameto the same conclusion, though he doubted whetherthe epiglottis covered the larynx completely.Johnstone (1942) published excellent still radio-graphs, showing beyond all doubt that the epiglottisturned down. He referred to the findings of Welin(1939) who believed that some cases of dysphagia,having the sensation of something sticking in thethroat, were due to the slow return of the epiglottisto the upright position. Johnstone considered thatit would be necessary to employ some form of kine-radiography before a full understanding of thesequences of movements could be obtained.

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Further reference to the paper by Stuart andMcCormick (1892) reveals that it is not a full report.It is quite clear that they were unable to keep theepiglottis under observation in all phases of swallow-ing, a point which is borne out by the report ofIredell, a laryngologist, quoted in the subsequentpaper by Stuart (1892). Moreover, Johnstone (1942)contradicted their findings, stating that he observeda similar patient with an open pharynx and saw theepiglottis turn over.

Why should the tongue of the epiglottis be turneddown during swallowing? In only two instances inover 500 examinations have we seen the down-turned epiglottis acting as a true cover valve, i.e. as aflap covering the entrance to the wide open larynx, sopreventing the entrance of a bolus into the larynx(Fig. 7). In a previous paper (Kemp, 1950), it wassuggested that the epiglottis acts as a valve toprevent particles of food being swept into the larynxduring the phase of reaeration of the airways, afterswallowing has been completed. In support of thistheory it has been noted that there was frequentlya residue retained upon the upper surface of theepiglottis, which if the epiglottis had not beenpresent, would presumably have been deposited overthe mouth of the larynx (Fig. 4b). The behaviourof Capps' patient appears to confirm this theory.

As a result of these investigations we now feelthat we can claim that the epiglottis is not a uselessstructure. It serves a very useful purpose during theact of swallowing, by assisting in the protection ofthe airway. It first acts as a ledge to receive the bolusinto the mesopharynx, and so obviates the necessityfor early closure of the larynx. Then after the phaseof vallecular arrest it becomes folded on itself, as ahood over the entrance to the larynx; the sides formchutes sloping into the lateral food channels andguide the bolus away from the laryngeal entrance.Though it does not normally act as a cover valve inthe old sense of the word, it does project over theentrance to the larynx when the larynx is tilted back-wards. Finally, it acts as a cover to prevent thedeposition of a residue of food over the mouth of thelarynx and fouling of the larynx during re-establish-ment of the airway. Without the epiglottis man is ata considerable disadvantage, even though he is ableto swallow without difficulty.

ACKNOWLEDGMENTSWe wish to acknowledge the help of our assistants, Miss

E. Emrys Roberts and Mr. M. S. Tuckey, without whomthis work could not have been carried out. Our thanks are

extended to the many members of the Staffs of the RadcliffeInfirmary and Institute of Social Medicine and others whoacted as volunteers. We are also grateful for the help andencouragement of Mr. Ronald Macbeth, and for assistanceafforded by Dr. Graham Weddell and Mr. F. Capps.

We are grateful to the editor of the Proceedings of theRoyal Society of Medicine for permission to reproduceFigs, lb, 3a, 4a, 4d, 4f.

SUMMARYThe protection of the larynx during swallowing depends

upon a number of factors:(1) The epiglottis acts as a ledge to check the descent of

the bolus, thereby obviating the necessity for early closureof the larynx.

(2) Elevation of the larynx results in the lumen of thelaryngeal vestibule being narrowed and arched backward.

(3) The bulk of the bolus is normally deviated to one orboth sides of the larynx, down the lateral food channels.

(4) When the bolus is passing down the lateral foodchannels, the vestibule may be still open and in communi-cation with air in the hypopharynx. Barium often enters thevestibule at this stage.

(5) The epiglottis is bent downward to form a hood overthe entrance to the larynx, but is not closely applied to theentrance to the larynx until the last of the bolus leaves thepharynx.

(6) Closure of the larynx is effected by contraction of thesphincteric girdle of muscle which surrounds it, and canoccur without the need for the larynx being raised. Thelarynx may be closed at any stage during the act of swallow-ing. Complete closure is always effected when the last of thebolus leaves the pharynx; any barium which has entered thevestibule of the larynx is squeezed out at this stage.

(7) The epiglottis prevents the deposition of a residue offood over the entrance to the larynx and upon reinflation ofthe airway carries the residue upwards into the vallecula.

(8) If the epiglottis be removed reinflation of the airwayis delayed until all traces of food have been removed fromthe entrance to the larynx by repeated acts of swallowing.

REFERENCESARDRAN, G. M., and KEMP, F. H., Proc. Roy. Soc. Med.,

1951, xliv, 1038.ARDRAN, G. M., and KEMP, F. H., and MANEN, L. (to

be published).ARDRAN, G. M., and TUCKEY, M. S., Journ. Physiol.,

1951, cxii, 28, P.ARDRAN, G. M., and TUCKEY, M. S., Brit, jfourn Rad.,

1952, xxv, 33.BARCLAY, A. E., The Digestive Tract, 1933 and 1936 (The

Cambridge University Press).COWGILL, G. R., Howell's Text Book of Physiology, 1946

(W. B. Saunders & Co., Philadelphia).FRENCKNER, P., Act. Oto. Lar., 1949, Suppl. lxxviii, 83.HEGNER, K., Arch. Oter . . . Heilk, 1936, cxl, 387.HURST, A. (1942). Personal communication.JANKER, R., Fortschritte A.D.G.D. Rontgenstrahlen, 1950,

lxxiii, 652.JOHNSTONE, A. S., Journ. Anat., 1942, lxxvii, 97.KEENE, M. F. L., and WHILLIS, J., Anatomy for Dental

Students, London, 1950, (Edward Arnold & Co.)KEMP, F. H., Jfourn. Physiol., 1951, cxii 11. P.MAGENDIE, F., Compendium of Physiology, 1823, 191-6.MOSCHER, H. P., Laryngoscope, 1927, xxxvii, 237.NEGUS, V. E., The Mechanism of the Larynx, 1929 and

1949 (Heinemann).RAMSEY, G. H. S., Radiology 1949, ]ii, 684.REYNOLDS, R. Personal demonstration of cineradio-

graphic films.STUART, T. P. A., and MCCORMICK, A., Journ Anat.,

1891-2, xxvi, 231 (London).STUART, T. P. A., Proc. Roy. Soc, 1891-2, i, 323

(London).WELIN, S., Acta. Rad., 1939, xx, 482.

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