roup of muscles
approximate the cords, while another muscle makes them tense.]

_The Larynx_.--The larynx is situated at the top of the sound-pipe (trachea
or windpipe), and consists of a framework of cartilages articulated or
jointed with one another so as to permit of movement (_vide_ fig. 4). The
cartilages are called by names which indicate their form and shape: (1)
shield or thyroid, (2) the ring or cricoid, and (3) a pair of pyramidal or
arytenoid cartilages. Besides these there is the epiglottis, which from its
situation above the glottis acts more or less as a lid. The shield
cartilage is attached by ligaments and muscles to the bone (hyoid) in the
root of the tongue, a pair of muscles also connect this cartilage with the
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