There are only three accessory muscles of the scapula, and these are the Levator Scapulae Ventralis, Teres Major, and the Teres Minor.
Levator Scapulae Ventralis
This is a flat, band-like muscle lying on each side of the neck, just between the clavotrapezius and acromiotrapezius muscles.
Teres Major
The Teres Major is the stout muscle just below the infraspinatus muscle . Origin, axillary border of the scapula, Insertion, medial surface of the humerus, Action, rotates the humerus inward and lowers it.
Teres Minor
The Teres Minor is situated just under the infraspinatus muscle. It is triangular-shaped. Origin, axillary border of the scapula, Insertion, greater tuberosity of the humerus, Action, assists the infraspinatus to rotate the humerus.