Throughout the body, there are several points at which blood vessels unite. The junctions are termed anastomoses. In the simplest sense, an anastomosis is any connection (made surgically or occurring naturally) between tube-like structures. Naturally occurring arterial anastomoses provide an alternative blood supply to target areas in cases where the primary arterial pathway is obstructed. They are most abundant in regions of the body where the blood supply may can be easily damaged or blocked (such as the joints or intestines). This article focuses on the arterial anastomotic networks of the upper limb.