THE GLOTTIS.

ONE Friday in august 1873, while watching a large python, at the Zoological Gardens, swallowing a duck which it had just killed, I was struck by a singular something projecting or hanging from the side of the snake’s mouth. It looked like a kind of tube or pipe, about one inch and a half or two inches of which were visible. The python had rather an awkward hold of the duck, having begun at the breast with the neck doubled back, the head forming some temporary impediment to the progress of the jaws upon the prey. So the strange protuberance gave one a ‘sort of turn,’ and a shudder. It looked as if it might be some part of the crushed bird, and then again it had the appearance of some internal arrangement; and another shudder crept over one as the idea suggested itself that the poor snake had ruptured its throat in some way. What could this queer thing be, hanging on one side, as you see the tongue of a horse or dog sometimes lolling sideways over its lower jaw? While intently pondering and observing this strange tube-like object, in size somewhat as big as the edge of a thimble, I saw the end of it moving of itself, an orifice contracting and closing tight, by the loose skin puckering up, so to speak. Presently it opened, and by and by again closed tight, as you see the breathing orifice of the octopus contract and expand, open and close, at regular intervals, only in the present case the intervals were not regular. This strange tube, then, had life and volition in it! What could it be?

Suddenly a certain day of one’s childhood flashed into my mind, and a certain scene of home. One Michaelmas Day it was, when, having stolen surreptitiously into the kitchen to coax the cook to ‘let me see the goose!’ I found her busy preparing the bird, and clambered into a chair to watch her. ‘What’s that?’ I demanded, seeing part of a long, pipe-like looking thing lying there.

‘Oh, that’s the windpipe. That’s like what you’ve got in your throat; and that’s where the crumbs get to make you choke so,’ in allusion to a recent occurrence.

I gazed with awe and interest at that very strange thing, and wondered if it really could be like anything in my own throat, and where it began and ended, and so on. And that goose’s windpipe was indelibly stamped on my memory.

And now that scene came vividly back to me, for there was a windpipe sort of look about this appendage to the snake’s jaw, only it did not appear to be bruised or injured in any way. Nor from the position of the duck (by this time half swallowed) could it belong to the bird. And, again, it moved with an independent motion!

And now the snake threw up its head, to free the legs of the duck from its folds where it had been held, and as you see horses toss up their heads to get the grain in the bag hung on their noses, and I saw the tube-like object still more plainly. Then, with a strange, awe-struck feeling, came a conviction that this could be nothing less than the poor snake’s windpipe, and that something must be very wrong with it.

I beckoned to the keeper, and pointed to it, telling him, ‘I do think that must be its windpipe. Is it hurt?’

The keeper said, ‘No, the snake was not hurt. That he had often seen it like that when the snakes were feeding; and that he also thought it must be the windpipe, to enable the snake to breathe while feeding.’

Next day, with eager steps and excited curiosity, I hurried to the British Museum reading-room, thinking I had made a wonderful discovery, for I had never heard this strange phenomenon alluded to, and the keeper evidently knew very little about it.

With this great secret on my mind, I flew to the well-known shelves, to secure those books which would certainly enlighten me if information were to be had. Alas! for my wonderful discovery, though it really had been a portion of the windpipe which was thus extended from the mouth, it was what had been known long ago by those physiologists who had studied the anatomy of the ophidia, and it was as coolly described as if it were the commonest occurrence in the world for creatures to do what they pleased with their windpipe!

Says Professor Owen in his Anatomy of the Vertebrates, vol. i. p. 525: ‘The glottis of serpents can be drawn forward and protruded from the mouth by the action of’ (certain surrounding) ‘muscles. In marine serpents the glottis is situated very near the fore part of the mouth, and the air can be inspired at the surface of the water without exposure of the jaws.’

The lungs of snakes, then, are supplied with air through that moveable tube, and the ‘glottis,’ which is the mouth or opening of what may here be called the air-tube, not to venture on scientific terms, was what I had seen ‘puckered up,’ as it appeared.

We may briefly remind the reader that our own throats contain two passages, one to the lungs, the other to the stomach; and in order that the air passage may be safely guarded from the entrance of any foreign particles, there are various parts, valves, and muscles which come into play with the action of swallowing, each and all having technical names, larynx, pharynx, glottis, epiglottis, etc., which need not be here described. But in the adaptive development of those wonderful creatures, snakes, the entrance or mouth of the windpipe—which begins in their mouth—can not only be closed at will, but still further to protect the passage, and also to enable the reptiles to breathe during the long process of swallowing, they can absolutely bring the apparatus forward, even beyond their mouths; and this was what had so surprised me on witnessing it.

The glottis, being the soft, membranous end or aperture, was what opened and closed, expanded and contracted, by that sort of puckering up and loosening again that was observable, and which here was rounded, but in the higher animals is a narrow, lip-like slit.

Some physiologists, in describing this ‘air-tube’ of serpents, speak of it as the larynx, which is what we unscientific folk would call the entrance to, or the upper portion of, the true windpipe or trachea. Others, again, affirm that they saw the ‘windpipe’ projecting. After all, much less has been said about it than one could wish; and what is said is somewhat conflicting, perhaps on account of the obscurity connected with this surprising adaptation of means to necessities. A thorough examination of the position of the trachea of snakes while feeding, and a perfect realization of its functions, could only be obtained were it possible to arrest the process of feeding by the instantaneous death of the feeder, and while every muscle of the snake’s mouth remained in position. Even then, one could not be positive, as snakes are endowed with the astonishing power of carrying out their intentions, or, in common language, ‘going on with their business,’ even after death. That is to say, owing to the irritability of their muscles, the action which they were about to perform (as, for instance, springing at a foe) continues should the head be shot off at the moment of making the attempt. In p. 56 and chap. xxi. some remarkable elucidations of this are given.

The general appearance of a windpipe is familiar to every one. It is formed of a series of rings or hoops, partially cartilaginous in mammals; that is to say, they are incomplete behind, where their ends are united by muscle and membrane, and come in contact with the gullet; but in serpents the rings are entire, the ends of each being joined together by an elastic substance. The rings themselves are also connected with each other by elastic membranes, so that the windpipe is capable of being extended like an india-rubber tube, and of regaining its former position.

The length of it naturally varies according to the size and species of serpent; but as a rule it is always much longer comparatively than in man. In a full-sized rattlesnake, the trachea is about twenty inches long. In a boa constrictor, also, though a much larger snake, it measures about the same. In smaller snakes it is, of course, much shorter; but there is the same singular diversity in this as we find in other serpent anomalies, viz. a great variation in the length in snakes of equal size, and without any very apparent reason.

Bingley, in his Animal Biography, 1820, describes the appearance of a large snake (M’Leod’s celebrated boa) when gorging a goat; but the account, like those of that time, is more sensational than scientific. ‘His cheeks were immensely dilated, and appeared to be bursting, and his windpipe projected three inches beyond his jaws.’

Broderip, a few years later, 1825, more lucidly and dispassionately describes what he had observed. ‘I have uniformly found that the larynx is, during the operation of swallowing, protruded sometimes as much as a quarter of an inch beyond the edge of the dilated lower jaw. I have seen, in company with others, the valves of the glottis open and shut, and the dead rabbit’s fur immediately before the aperture stirred, apparently by the serpent’s breath, when his jaws and throat were stiff, and stretched to excess’ (Zoological Journal, ii. 1826). This account is quoted from the paper entitled, ‘Some Account of the Mode in which the Boa Constrictor takes its Prey, and of the Adaptation of its Organization to its Habits,’ by W. J. Broderip, Esq., F.L.S. The paper was written as a criticism of the M’Leod story.

I, also, on several occasions, saw the fur or feathers stirred by air when the mouth or valve opened of what we may safely call the air-tube, whether larynx or trachea.

Though so rarely mentioned in popular books on snakes, this surprising modification of the breathing apparatus was described by the indefatigable Dr. Edward Tyson, on his dissection of the first rattlesnake that fell into the hands of the Royal Society, 1683, and whose paper on the Vipera caudisona, as he named it, is quoted in chapters xvi. and xx. ‘Over the tongue did lye the larynx, not formed with that variety of cartilages as is usual in other animals, but so as to make a rime or slit for receiving or conveying out the air. Nor was there any epiglottis for preventing other bodies from slipping in, this being sufficiently provided for by the strict closure of it.’[38]

Dr. Tyson examined only a dead specimen, and could not therefore witness the action observable in life; but his remarkable accuracy in describing the parts will be evident in comparing what he said with Dumeril, who did observe the living reptiles. The confusion which sometimes occurs in distinguishing the parts may be also explained by the less complicated structure of the tube, which in higher animals presents the nicer distinctions of the parts, glottis, epiglottis, larynx, etc.

‘Il n’y a pas de vÉritable larynx, une petite languette mobile qui s’ajuste, sur l’ouverture linÉaire; c’est la glotte.... La glotte, situÉe au-dessous de la victime, se porte en avant, et l’acte de respiration ne se trouve point empÊchÉ. C’est que nous avons indiquÉ À l’article de la dÉglutition; car on voit distinctement alors la glotte se fermer et se dÉlater.’[39]

This petite languette became a new object of curiosity, and soon came fresh opportunities for observation, namely, when some of the larger snakes were engaged in yawning. On account of its extreme mobility, you do not always detect the form of this little point on the upper lip, which as often as not presents a rounded opening; but occasionally the little tongue—which can be nothing but an apology for an epiglottis—is very distinct, and may be compared with the moveable, pointed snout of some of the large pachyderms, or, still better, with an exactly similar formation at the end of the elephant’s trunk, and which, though for a different purpose, moves similarly.

As to the exact position of this glottis when at rest, a word or two must be said; for a number of prepositions have been used to describe it. One writer says ‘beneath’ the tongue sheath, others say ‘beyond,’ others again ‘before;’ ‘over,’ ‘above,’ ‘behind,’ ‘in front of,’ have been variously used, and all depending on which way the snake is viewed; but without drawing upon half a score of prepositions to puzzle the reader, as I myself was sorely puzzled until a yawning snake was so kind as to afford me an ocular scrutiny of its lingual arrangements, we can easily comprehend where a passage to the windpipe and lungs must necessarily be, and which, it is clear, is not under the tongue. When a snake’s head is raised, as in crawling up a wall or a tree, the glottis may be said to be ‘beneath’ or ‘under;’ but the general position of a snake being horizontal, the mouth then opened would show you the opening of the tongue sheath nearest to you and to the front; and beyond that, behind, over, or upon the tongue sheath, is another aperture, which is the glottis or entrance to the larynx and trachea or windpipe.

So there are in fact two sheaths or tubes lying one upon the other, viz. the tongue sheath, and upon this and parallel with it, the windpipe.

After becoming better acquainted with the nature of that tube which had impressed me so strangely, I lost no opportunity of making further observations, and on the following feeding day at the Gardens I saw the air-tubes of several snakes plainly. In September of that year, a new ‘Horseshoe’ snake (Zamenis hippocrepis) arrived from Morocco. It was a small and very pretty snake, and while enjoying the privilege of a private inspection, the keeper got its mouth open for me, enabling me to see the glottis, as well as to both see and feel the four upper rows of its beautiful little teeth, closely placed, and as sharp as the finest pins. But the action of the air-tube was very distinct. Probably little Zamenis was breathing harder and nervously under the detention, but no word better describes the formation of the aperture of the perfectly rounded tube, and the movement of it, than the petite languette.

Subsequently, there were opportunities of observing the air-tube in two of the large African vipers, the ‘River Jack’ or ‘Nose-horned’ vipers (Vipera rhinosceros) occupying the same cage. Each struck a guinea-pig and held it. One of them began to eat his before it was quite dead, and had finished it before his friend had begun. In his case, the air-pipe was at the side of his distended jaws. In the other, it projected more than half an inch beneath, nearly in the centre.

This happened on a mild, damp day in November 1873, and after that I saw the tube in ‘several snakes,’ but I regret the names were not entered in my notebook at the time. In the smaller non-venomous snakes, or in the lacertines—of which there were then a large number—I do not remember to have observed it. They despatch their frog or mouse so quickly that they would scarcely need a fresh supply of air meanwhile. In the larger vipers, rattlesnakes, and constrictors, the air-tube was undoubtedly witnessed. Winter then terminated my observations, and afterwards a prolonged absence from town. Unfortunately, when observations were about to be resumed, the change of the plans at the Zoological Gardens, and the exclusion of the public, defeated my intentions, though on one occasion I did see the windpipe of little Natrix torquata very distinctly; and this was the smallest snake in which I had ever observed it. Natrix had nearly disposed of a large frog. The whole of it was in his mouth, which was widely expanded, and the air-tube was protruded sideways, not out of the mouth, but sufficiently forward to enable one to distinguish its form, and the action of the petite languette. The prey being unusually large, the snake had needed air while swallowing it.

On several occasions in snakes recently dead, and of various sizes, one has been able to notice how admirably this tube, which lies along the mouth like a soft cushion, somewhat in the form of a parrot’s tongue, is supplied with space in the roof, arched to fit it, the palate teeth enclosing it on each side, while the opening, or glottis, exactly meets the nostrils, les arriÈres nez, bringing it into communication with the outer air.

In a little Coluber, just dead, I again had an opportunity of making observations. The membranous coating was so thin and transparent that the rings of the windpipe could be very distinctly traced from a quite forward position in the mouth, and beginning on and over the tongue sheath. The surrounding skin or membrane was also loose and abundant, so that with the point of a needle the upper part of the windpipe could be easily drawn forward beyond the lips. In life the little snake could thus have voluntarily protruded it as occasion required.

Another day the large reticulated python seemed to intentionally gratify my curiosity by affording me a most leisurely and excellent opportunity for observation. His head was raised, and so close to the glass that the process of swallowing could be watched conveniently. The final swallow, or successive efforts at the last were, as usual, attended with frequent yawns. The glottis, as could on these occasions be distinctly seen, was repeatedly opened and closed, and after being extended beyond the mouth, it gradually resumed its natural position. While the prey occupied the entire space between the gaping jaws, one could see the air-tube pushed forward beneath; but as by degrees the duck disappeared down the throat, the interior of the mouth could be better and better observed. In this large snake the membrane or skin was too thick to enable one to discern rings as in the little Coluber; but as the larynx is merely the upper part of the trachea, and as the glottis is the mere membranous opening to the larynx, it seems evident that the windpipe itself is also extensible, the windpipe being, indeed, the only portion of the air-tube sufficiently firm and resisting to aid the purpose of respiration under such conditions.

The exact distance which the tube is extended cannot be accurately stated. It would not be equally protruded in snakes of different sizes nor under different conditions. Broderip saw it ‘as much as a quarter of an inch.’ Bingley, an earlier and a less safe authority, says ‘the windpipe projected three inches beyond his jaws.’ The keeper at the Gardens thought he had sometimes seen it ‘as much as two inches in the largest snakes;’ and my own impression was, one inch, at least, in the python, and almost that in the large vipers.

It is undoubtedly one of those interesting features worthy of further investigation, and one is surprised that more accurate information regarding it has not appeared in our later encyclopedias and in the ‘Proceedings of the Zoological Societies.’

So long ago as 1826, it was observed and confirmed by the distinguished author of Zoological Researches, and Leaves from the Notebook of a Naturalist. The author of British Reptiles, who conducted the Zoological Journal when Mr. Broderip contributed the valuable paper above quoted, added a note by special request, stating that his own ‘not unfrequent observations have on every point been completely confirmatory of those above recorded’ by W. J. Broderip, Esq.

A very good account of the whole is quoted in the Penny Magazine, 1836, and we are therein further enlightened by reading that Joseph Henry Green, Esq., F.R.S., in one of his lectures at the Royal College of Surgeons, alluded to Broderip’s paper ‘On the Mode in which Constrictors swallow their Prey,’ and which had drawn his attention to the statement about the larynx, and led him to examine the mouth of a snake.

In process of dissection, he detected two muscles in the lower jaw, evidently intended for the purpose of bringing the larynx forward; how far forward and how much of the true windpipe was also brought forward, he did not say. But this in a dead specimen could scarcely be affirmed with certainty.

From the large size of their prey, and the jaws being stretched open and gorged to their utmost capacity, it is plain that snakes cannot breathe freely in the ordinary manner while feeding, a process sometimes of an hour or more. Owing to the construction of their lungs and their capability to contain a large volume of air, they do not require to breathe frequently; still they do occasionally take a fresh inspiration, and their needs are met by this wonderful arrangement of the breathing apparatus.