Radial artery cannulation site, illustration. The radial artery of the wrist is typically chosen as the site to insert an indwelling arterial catheter to monitor a patient's blood pressure and other vital signs and measurements. This illustration shows the anatomy of the wrist and the location of a branch of this artery. At left are parts of the ulna and radius bones. The thenar muscles at the base of the thumb are shown, as are the tendons of the flexor carpi radialis and abductor pollicis longus muscles.