Figure 11. Centrale bone as a keystone in the carpus.

(A) Plica umbra grasping a narrow branch. On the right hand, the first cleft surrounds the branch. On the left hand, the third cleft surrounds the branch. A detail of the right hand shows the approximate arrangement of the carpal and metacarpal during grasping. Photo: Rafael Balestrin. (B) Detailed diagram of (A). Three muscles are shown: extensor carpi ulnaris (green); extensor ant ebrachii et carpi radialis (orange); extensor digitorum (pink). (C) Human arm showing the relationship between the capitate and the forearm muscles (modified from Neumann (2010)). Three muscles are shown: extensor carpi radialis longus and brevis (yellow); abductor pollicis longus (green); extensor pollicis longus and brevis (pink). Note that the centrale bone in grasping lizards hands exhibit the same form, position and probably mechanical role as the capitate in human hands. Both, the centrale and capitate probably act as keystones and control the axis of rotation.