Thoracoacromial a.

The thoracoacromial artery (or trunk) is a short artery that arises from the second part of the axillary artery posterior to the superior part of the pectoralis minor m.

Projecting forward to the upper border of the pectoralis minor, it pierces the clavipectoral fascia and divides into four branches—pectoral, acromial, clavicular, and deltoid.