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cartilages; it is widely opened during inspiration, and during deglutition is shielded by the epiglottis, which, falling backwards and downwards, closes it like the lid of a box.

The vocal cords, or thyro-arytenoid ligaments, are 4 in number-2 at each side. The false, or superior, are wide and loose, and are divided from the true, or inferior, by a space termed the ventricle, from which a small cavity leads off, the sacculus laryngis of Hilton, of use in secreting mucus to lubricate the cords. Each true cord arises from the concavity of the thyroid cartilage, and is inserted into the anterior angle of the base of arytenoid cartilage; the thyro-arytenoid muscle lies along its outer edge, and adheres to it. It is composed of yellow elastic tissue, and measures about

of an inch, or somewhat less in the female. Voice is due to their vibration, excited by the air as it is expired, a fact first stated in 1741 by Ferrein. The cords converge in front, and leave a triangular space between them, the rima. When the organ is quiescent, their surfaces are not parallel to the column of air, but during vocalisation they become so, as demonstrated by the Rev. Prof. Willis, of Cambridge-owing, as he believed, to the action of the thyro-arytenoid muscles. Prof. Croker King, late of Queen's College, Galway, has proved, by experiment and most ingenious arguments, that this parallelism is mainly effected by the oblique fibres of the arytenoid muscle, which constitute part of a bent lever of the first order. He describes, as follows, the effect on the vocal cords of the motions of the arytenoid cartilages: "The forward motion will relax and the backward movement will stretch the vocal cords; the rotation in a direction outwards on the vertical axes will separate, and the rotation inwards will approximate the vocal cords; the rotation on the horizontal axes, inwards and outwards, will cause the anterior spur to revolve, and to carry with it the vocal cord, which will thus

alternately incline towards and from the cord of the opposite side." His valuable paper will be found in the "Transactions of the Royal Irish Academy for 1849." The cords are but from to of an inch asunder when vocalising. Areolar tissue seems to be absent between the mucous and elastic layers of the cords, as I have seen illustrated in cases of laryngitis, for the œdema does not extend below them. Such lax tissue would

probably interfere with their vibration.

The muscles of the larynx and their actions are thus tabulated by Todd and Bowman:

Crico-thyroidei. stretch the vocal cords

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relax and place the vocal

Thyro-arytenoidei.cords in the position for

Crico-arytenoidei

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Crico-arytenoidei laterales

Arytenoidei

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vocalisation

separate the front of the

arytenoid cartilages

press together the front of

the arytenoid cartilages

govern pitch of notes

open

f glottis

govern

aperture

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S press together the back of glottis glottis the arytenoid cartilages

The muscles, cartilages, and cords concerned in vocalisation, are represented in the bird's-eye view of the organ on the following page, and their relative position should be carefully studied in order to comprehend the exquisite mechanism of the organ.

The larynx is supplied by 2 branches of the pneumogastric-the superior sensitive, which serves to test the air; and the inferior, or recurrent laryngeal, which supplies all the muscles save the crico-thyroid, to which the spinal accessory sends a branch, accompanying the superior laryngeal. Section of the inferior will prove fatal by paralysing all the muscles, and the falling together of the arytenoid cartilage and cords produces apnoea. The larynx has been compared to every variety of musical instrument-the stringed, as the violin; the wind, as the trombone; but to those which produce sound by the vibration of a tongue-as the hautboy, accordeon,

&c.-it bears most resemblance. When the cords are tense they vibrate rapidly, and a high note is produced;

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when relaxed, fewer vibrations, and a lower sound. A string, made tense by a given force, will vibrate twice as rapidly if the force be multiplied 4 times; but in the larynx there are so many modifying circumstances, these results do not exactly hold good. Willis constructed an artificial larynx, in which strings of caoutchouc represented the vocal cords; and, with the head of a subject arranged as here sketched, many vocal sounds can be imitated, and the effect of tension or relaxation, approximation or separation of the cords determined. The laryngoscope, so much improved by Prof. Czermak, will assuredly improve our knowledge of the physiology, as it

has the pathology of the organ of voice. When that physiologist visited Dublin, the effect of an aortic aneurism, in paralysing one side

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of the organ by pressure on the left recurrent nerve, was readily seen in a patient of mine.

The pitch of the human voice varies with the length, tension, and elasticity of the cords, and with the expiratory power of the chest. In singing, the vibrations succeed each other with exactly uniform rapidity. The following scale shows the range of the male voice (bass, barytone, and tenor), and that of females, males before puberty, and eunuchs (alto, mezzosoprano, and soprano).

The number of double Head and Trachea of a subject, with weights attached to produce degrees of tension of vibrations per second the vocal cords.

which take place during the exercise of each kind of voice is noted. The concert pitch of the principal London orchestras has been shown by Mr. Donovan to be nearly 450. The compass of the human voice extends from 1 octave to 3, which Catalani is said to have possessed. About 300 notes can be produced between the successive tones, a power peculiar to the human voice. Falsetto notes are produced by the inner edges or anterior half of the cords alone vibrating. So great is the variety of voice that the old and young, male and female, and different individuals, may be dis

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tinguished by a peculiar tone; and the vocal cords and

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176-704

264-1056

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