the syrinx, which are the real vocal muscles, vary in number
in different groups, reaching their maximum in the true
Passeres, which have always five pairs. These are represented
in their natural position in Figs. 8-10, giving a front, back
and side view of these parts in the Kaven, while Fig. 11
repeats the last hut shews three of the five pairs partly
displaced to render their superior attachment more obvious.
To describe these muscles more particularly it may he said
that two pairs of them have a common origin about the
middle of the trachea, and, descending on its outside, divide
at a short distance above the end of the tube; one of them
—the long posterior tensor (ƒ), being directed downward and
backward, is inserted at the extreme posterior end of the
first half-ring of the bronchus, while its counterpart—the
long anterior tensor (e), passing from the place of separation
downward and forward is inserted below the extreme point
of the last ring of the trachea. Within the angle formed
by the divergence of each of these pairs, a third slender and
cord-like muscle—the sterno-tracheal (d) arises on each side
and goes off to he inserted in the sternum. The fourth pair
—the short posterior tensor Qi) is the smallest of all, and,
arising near the middle of the lower end of the trachea,
its fibres, directed obliquely downwards and backwards, are
inserted on the extremity of the first of the incomplete
rings of the bronchi. The fifth pair—the short anterior
tensor (g) springs like the last from the middle of the
trachea, hut is somewhat larger and thicker, appearing as
though made up of several small muscles in close contact.
Its direction is obliquely downward and forward; it is
partly hidden by the long anterior tensor (e), and, attached
by a broad base to the last ring of the trachea and to the
cartilage immediately below, it reaches the extreme end* of
the first or second of the bronchial half-rings.
Thus while the lungs govern the volume of air as well as
the force with which it is expelled, the syringeal muscles
* As before stated, in the other great division of Passeres—Prof. Garrod’s
Mesomyodi—none of which are British or even European, such forms as possess
muscles that reach to the bronchi, have their muscles joined to the middle and
not the extremity of the bronchial half-rings.
influence both the diameter and the length of the bronchi,
and the absurdity of the vulgar belief that to enable a bird
to “ speak ” the slitting of its tongue is necessary ought
F ig. 8.
Fig. 9.
Fig. 10. Fig. 11.
hereby to be manifest. The principle on which the vocal
organs in Birds are framed is that which prevails in wind-
instruments generally; the notes in the ascending scale being
produced by a corresponding contraction of the diameter or
the length of the tube, and vice versa.