The Posterior Circumflex Artery is a little smaller than the preceding vessel, and arises close to it from the posterior part of the axillary artery in its third stage : immediately after its origin it sinks into a quadrangular space, bounded above by the sub-scapular and teres minor muscles, inferiorly by the tendons of the teres major and latissimus dorsi, anteriorly by the humerus, and posteriorly by the long head of the triceps : in passing through this space it winds round the surgical neck of the humerus, accompanied by the posterior circumflex nerve. After giving a few branches to the teres minor and sub-scapularis muscles, and to the shoulder-joint, it sinks beneath the deltoid muscle, into which it sends numerous branches, which anastomose with the supra-scapular, acromial, and anterior circumflex arteries.