As it can be seen in the pictures below, both
muscles are well positioned to cause the inferior angle of the scapula to move laterally around the
thoracic wall. The clavicle acting as
a strut restricts movement at the acromion process, so that the overall effect
of the action of these two muscles is to elevate the acromion process and move
the inferior angle laterally, thereby enabling the glenoid fossa to face more
directly upwards. This movement of the pectoral girdle is extremely important
for increasing the range of movement possible, particularly in terms of
abduction and flexion of the upper limb at the shoulder.
Trapezius contributes to the rotation by contraction of
its upper fibres which lift the lateral end of the clavicle and acromion process upwards while at the same time its
lower fibres pull downwards on the medial end of the spine of the scapula.
Serratusanterior, the more important
of the two muscles in this movement, pulls strongly on the inferior angle of
the scapula, where the majority of
its muscle fibres insert, to pull it laterally around the chest wall. The
notional axis about which this rotation takes place is just below the spine of
the scapula towards the base.
Resultant movements are shown in the picture below.
Serbian Dinar Exchange Rate
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