The way in which the giant panda, Ailuropoda melanoleuca, uses the radial sesamoid bone - its `pseudo-thumb' - for grasping makes it one of the most extraordinary manipulation systems in mammalian evolution. The bone has been reported to function as an active manipulator, enabling the panda to grasp bamboo stems between the bone and the opposing palm,. We have used computed tomography, magnetic resonance imaging (MRI) and related techniques to analyse a panda hand. The three-dimensional images we obtained indicate that the radial sesamoid bone cannot move independently of its articulated bones, as has been suggested, but rather acts as part of a functional unit of manipulation. The radial sesamoid bone and the accessory carpal bone form a double pincer-like apparatus in the medial and lateral sides of the hand, respectively, enabling the panda to manipulate objects with great dexterity.