iding over synergic groups of muscles
habitually brought into action for this simplest form of vocalisation,
connected with the primitive emotion of anger.

I will now consider at greater length each part of the vocal instrument.

I. THE BELLOWS

[Illustration: Fig 1]

[Description: FIG. 1.--Front view of the thorax showing the breastbone, to
which on either side are attached the (shaded) rib cartilages. The
remainder of the thoracic cage is formed by the ribs attached behind to the
spine, which is only seen below. The lungs are represented filling the
chest cavity, except a little to the left of the breastbone, below where
the pericardium is shown (black). It can be seen that the ribs slope
forwards and downwards, and that they increase in length from above
downwards, so that if elevated by the muscles attached to them, they will
tend to push forward the elastic cartilages and breastbone and so increase
the antero-posterior diameter of the chest; moreover, the ribs being
elastic will tend to give a little at the angle, and so the lateral
diameter of the chest will be increased.]

The bellows consists of the lungs enclosed in the movable thorax. The
latter may be likened to a cage; it is formed by the spine behind and the
ribs, which are attached by cartilages to the breastbone (sternum) in front
(_vide_ fig. 1). The ribs and cartilages, as the diagram shows, form a
series of hoops which increase in length from above downwards; moreover,
they slope obliquely downwards and inwards (_vide_ fig. 2). The ribs are
jointed behind to the vertebrae in such a way that muscles attached to them
can, by shortening, elevate them; the effect is that the longer ribs are
raised, and pushing forward the breastbone and cartilages, the thoracic
cage enlarges from before back; but being elastic, the hoops will give a
little and cause some expansion from side to side; moreover, when the ribs
are raised, each one is rotated on its axis in such a way that the lower
border tends towards eversion; the total effect of this rotation is a
lateral expansion of the whole thorax. Between the ribs and the cartilages
the space is filled by the intercostal muscles (_vide_ fig. 2), the action
of which, in conjunction with other muscles, is to elevate the ribs. It is,
however, unnecessary to enter into anatomical details, and describe all
those muscles which elevate and rotate the ribs, and thereby cause
enlargement of the thorax in its antero