Volume 1

Human physiology / by Robley Dunglison.

  • Dunglison, Robley, 1798-1869.
Date:
1856
Catalogue details

Licence: Public Domain Mark

Credit: Human physiology / by Robley Dunglison. Source: Wellcome Collection.

Provider: This material has been provided by Royal College of Physicians, London. The original may be consulted at Royal College of Physicians, London.

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    fulfils a similar office. At the same time, the genio-glossus, by apply- ing the tongue to the palate, from the tip to the roof, raises the os hyoides, the larynx, and, Avith it, the anterior paries of the pharynx. The same effect is directly induced by the contraction of the mylo- hyoidei, and genio-hyoidei muscles; which, instead of acting as de- pressors of the lower jaw, as they do during mastication, take the jaw as their fixed point, and are levators of the os hyoides. The larynx is thus elevated, carried forwards, and meets the bolus to render its passage over the aperture of the larynx shorter, and, therefore, more speedy. To aid this effect,—when we make great efforts to swallow, the head is inclined forwards on the thorax. Whilst the os hyoides and the larynx are raised, they approach each other,—the upper mar- gin of the thyroid cartilage passing behind the body of the hyoid bone: the epiglottic gland is pushed backward, and the epiglottis is depressed, and inclined backwards and downwards, so as to cover the entrance to the larynx. The cricoid cartilage executes a rotatory motion on the inferior cornua of the thyroid cartilage, which occasions the entrance of the larynx to become oblique from above to below, and, of course, from before to behind. The bolus thus glides over its surface; and, forced on by the veil of the palate, and by the constrictors of the pharynx, reaches the oesophagus. At one time, it was universally believed, that the epiglottis is the sole agent in preventing substances from passing into the larynx. The experiments of M. Magendie' have, however, demonstrated, that this is the combined effect of the motions of the larynx just described, and of the muscles, whose office it is to close the glottis; so that, if the laryngeal and recurrent nerves be divided in an animal, and the epiglottis be left in a state of integrity, deglutition is rendered ex- tremely difficult;—the principal cause, that prevented the introduction of aliments into the glottis, having been removed by the section. M. Magendie, and MM. Trousseau and Belloc^ refer to cases of individuals, who were totally devoid of epiglottis, and yet swallowed without any difficulty,^ and Magendie remarks, that if, in laryngeal phthisis with » destruction of the epiglottis, deglutition be laboriously and imperfectly accomplished, it is owing to the carious condition of the arytenoid cartilages, and to the lips of the glottis being so much ulcerated as not to be able to close the glottis accurately. Whilst the bolus, then, is passing over the top of the larynx, respiration must be momentarily suspended, owing to closure of the glottis; and if, from distraction of any kind, we attempt to speak, laugh, or breathe, at the moment of deglutition, the glottis opens, the food enters, and cough is excited, which is not appeased until the cause is removed. This is what is called, in common language, the food going the wrong way. As soon as the bolus has cleared the glottis, the larynx descends, the epi- glottis rises, and the glottis opens to give passage to the air. This is / ' Memoire sur I'Usage de I'Epiglotte dans la Deglutition, Paris, 1813; and Prt'cis, &o., i. G7. 2 A Practical Treatise on Laryngeal Phthisis, &c. &o. ; Dr. Warder's translation, p. 84, in Dunglison's American Medical Library, Philad., 1839. ^ A similar case is given by Targioni, in wliich neither deglutition nor speech was impaired ; Morgagni, xxviii. 13.