To study why the palmar capsular connections between radius and lunate remain intact in perilunate ligamentous injury of the wrist joint, and to compare the material properties of the short radiolunate, long radiolunate, and radioscaphoid region of the radioscaphocapitate ligaments (as the extrinsic ligaments) with those of the intrinsic ligaments of the previous papers, the anatomical and mechanical characteristics of those three palmar radiocarpal ligaments of twenty cadavers were measured and tested by a servo-hydraulic test machine. In spite of its small cross-sectional area (24% of short radiolunate ligament), the radioscaphoid ligament demonstrates a failure load of 58% and a stress of 260% of the short radiolunate ligament, and toughness similar to both the short and long radiolunate ligaments. This suggests that the radioscaphocapitate ligament may contribute as an initial constraint to perilunate injury. The failure load of the scapholunate ligament might be smaller than previously reported due to testing strain rate, which coupled with its short initial length may make it more vulnerable to injury at lower applied loads. The short radiolunate ligament, in spite of the largest width and cross-sectional area, has a failure load and toughness similar to the long radiolunate ligament. The material properties of short and long radiolunate ligaments may explain why the rest of the carpals persistently dislocate or fracture about lunate.