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Full text of "Diseases Of The Nose Throat And Ear"

144

THE LARYNX, BRONCHI AND OESOPHAGUS

Articulating with the upper border of the cricoid cartilage are the arytenoid
cartilages to which are attached the vocal cords. The aryjenoids are pyramidaL
inshajgejuid have an anteriorLprojection called the vocal process, to which the
vocal cords are attached, and a lateral projection called the muscular process
to which the main abducting and adducting muscles are attached (Fig. 61).
The crico-arytenoid joint and the cricothyroid joint are synovial joints and
may be affected by all synovial joint diseases. The arytenoids adduct and
abduct on the cricoid, closing and opening the vocal cords. The thyroid
cartilage moves in relation to the cricoid at the cricothyroid joint causing
lengthening and shortening of the vocal cords. The anterior end of each cord
is attached to the thyroid cartilage at the level of the epiglottis while the
posterior end is attached to the cricoid via the arytenoid (Fig. 59).

The epiglottis is composed of yellow elastic cartilage and never ossifies.
The thyroid and cricoid cartilages are hyaline and begin ossifying after the age
of 25 in a patchy fashion—this is well seen in radiographs of the neck in older
patients.

MUSCLES

One muscle abducts (opens) the vocal cords, two adduct (close) them, one
adjusts the length and two adjust the tension.

Posterior crico-arytenoid muscle. This paired muscle arises from the
posterior surface of the cricoid and is attached to the muscular process of the
arytenoid. As it contracts the arytenoid is rotated around its axis, the vocal
processes move laterally and the cords abduct (Fig. 61).

Fig. 61. To show action of posterior crico-arytenoid muscle (diagrammatic). In A the muscle 4 is at
rest, the vocal process 2 is pointing medially, the muscular process 3 lies further to the side and the
vocal folds 1 are only slightly separated. In B the muscles are contracted, tMfttonditions are reversed
and, tiie glottis is widely open.

Lateral crico-arytenoid muscle. This paired muscle arises from the lateral
part of the cricoid arch and runs obliquely posterosuperiorly to be attached to
the muscular process of the arytenoid. On contraction, the muscular process is
drawn anteriorly, the vocal process medially and the cords adduct and close
(F#. 62). This action is aided by the interarytenoid muscle which is unpaired
and is attached to the posterior surface of both arytenoids.

Cricothyroid muscle arises from the oblique line on the lateral surface of the
thyroid lamina and is attached to the anterior face of the cricoid arch. As it