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
(_vide_ fig. 5); it is of interest to note that this muscle has a separate
nerve supply to that of the abductor and adductor muscles.
[Illustration: FIG. 5
Diagram after Testut (modified), showing the larynx from the front.]
[Illustration: FIG.
Pages:
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41