The quadrangular space is bounded medially by the long head of the triceps tendon, laterally by the humerus, superiorly by teres major, and inferiorly by teres minor. It is traversed by the axillary nerve and the posterior humeral circumflex aery. The triangular space is medial to the quadrangular space and it is bounded laterally by the tendon of the long head of the triceps, superiorly by teres minor, and inferiorly by teres major. The circumflex scapular aery, which is a branch of the subscapular aery, traverses this space. The dorsal scapular aery and suprascapular aery contribute to the scapular anastomosis with the circumflex scapular aery, but neither of these vessels are in the quadrangular or triangular spaces.