sternum or breastbone. The ring cartilage is attached to the windpipe by
its lower border; by its upper border in front it is connected with the
inner surface of the shield cartilage by a ligament; it is also jointed on
either side with the shield cartilage. The posterior part of the ring
cartilage is much wider than the anterior portion, and seated upon its
upper and posterior rim and articulated with it by separate joints are the
two pyramidal cartilages (_vide_ fig. 4). The two vocal cords as shown in
the diagram are attached to the shield cartilage in front, their
attachments being close together; posteriorly they are attached to the
pyramidal cartilages. It is necessary, however, to describe a little more
fully these attachments. Extending forwards from the base of the pyramids
are processes termed the "vocal processes," and these processes give
attachment to the elastic fibres of which the vocal cords mainly consist.
There are certain groups of muscles which by their attachment to the
cartilages of the larynx and their action on the joints are able to
separate the vocal cords or approximate them; these are termed respectively
abductor and adductor muscles (figs. 5 and 6). In normal respiration the
posterior ring-pyramidal muscles contract synergically with the muscles of
inspiration and by separating the vocal cords open wide the glottis,
whereby there is a free entrance of air to the windpipe; during expiration
this muscle ceases to contract and the aperture of the glottis becomes
narrower (_vide_ fig. 10). But when the pressure is required to be raised
in the air passages, as in the simple reflex act of coughing or in
vocalisation, the glottis must be closed by approximation of the vocal
cords, and this is effected by a group of muscles termed the adductors,
which pull on the pyramid cartilages in such a way that the vocal processes
are drawn towards one another in the manner shown in fig. 7. Besides the
abductor and adductor groups of muscles, there is a muscle which acts in
conjunction with the adductor group, and by its attachments to the shield
cartilage above and the ring cartilage below makes tense the vocal cords