3rd. The Lid ([pl. V], 11) is an elastic cartilage which serves to close the voicebox in the act of swallowing, in order to protect it against any intruding foreign substances. The food we take has to pass over it, and it sometimes happens, when the lid has not been pulled down tight enough, that a particle of food enters the voicebox, in which case we say it has "gone the wrong way," and there is then no peace until the intruder has been got rid of, generally by a violent fit of coughing.
The lid, it is true, is not the only means of protection which the voicebox possesses. Professor C. J. Eberth, for instance, mentions (Archiv für pathol: Anatomie, vol. lxiii., p. 135, Berlin, 1868) the case of a woman who, upon dissection, was found to be entirely without the free upper part of the lid, which could alone cover the voicebox. She had never experienced any difficulty in swallowing, and it is therefore clear that with her the closing of some of the parts immediately below was sufficient to prevent the food from getting into the voicebox. But "the exception proves the rule," and in spite of this and other similar cases, the fact remains that the lid is obviously the first and most natural protector of the voicebox.
4th and 5th. We have thus far become acquainted with three cartilages out of the five. Let us now remove one plate of the shield, as though cutting it off with a knife ([pl. VII], 1 and 2), in order that we may look inside and see the remaining two cartilages which have hitherto been hidden by it. These are—
The Pyramids ([pl. VII], 1 and 2), so called because of their shape. Their bases are triangular and hollowed out; their sides taper upwards and terminate in points which are bent slightly backwards, and they have each two projections, one pointing forwards ([pl. VII], 3) and the other outwards and backwards ([pl. VII], 4). It will be convenient to have a special name for the projections pointing outwards and backwards, which we will therefore call the Levers.
The Pyramids are attached with their hollow bases to the borders of the ring ([pl. VII], 5), and they are capable of executing rotary movements with surprising freedom and rapidity. Their inner sides may be made to run parallel or to diverge. In addition to this they can be drawn towards each other, or away from each other, so that their summits may either be widely separated or brought close together.
The Vocal Ligaments are two ledges of elastic tissue covered with a very delicate membrane. Each one of them is connected along its whole length, on one side, with the shield cartilage. The vocal ligaments are attached by their hinder ends to those little projections of the pyramids which point forwards ([pl. VII], 3, 3), and by their front ends to the centre of the shield ([pl. VII], 6), where the two plates meet under a more or less acute angle.
Plate VII.
SIDE VIEW OF THE VOICEBOX, OR LARYNX, SHOWING THE INTERIOR OF IT, THE RIGHT PLATE BEING REMOVED.