Fig. 3. The ranges of motion and passive kinematics for the hindlimb and iliosacral joints of Rana pipiens. The location of the instantaneous center of rotation was determined about each joint axis. The white arcs overlying the joint images represent the range of motion about each joint axis. Red dots represent the locations of the instantaneous centers of rotation measured over this range of motion. The dotted lines show the x, y and z axis. The left column shows the ranges of motion and kinematics for the hip joint: top panel, flexion—extension of the femur F relative to the pelvis P; middle panel, abduction—adduction of the femur; bottom panel, external—internal rotation of the femur. The hip kinematics corresponded most closely to the kinematics of a ball-and-socket joint. The second column shows the ranges of motion and kinematics for the knee joint: flexion—extension of the tibiofibula T relative to the femur, abduction—adduction of the tibiofibula and external—internal rotation of the tibiofibula (Tibfib). Flexion—extension kinematics at the knee corresponded most closely to the kinematics of a rolling joint, while the kinematics about the other axes corresponded more closely to the kinematics typical of hinge joints. The top panels of the third and fourth columns show the ranges of motion and kinematics for ankle flexion—extension (rotation of the astragalus segment A relative to tibiofibula), and tarsometatarsal flexion—extension (rotation of the metatarsals M relative to the tarsals). The ranges of motion (ROMs) about the other axes of these two joints were minimal (<20°). Flexion—extension kinematics at the ankle corresponded most closely to the kinematics of a rolling joint. Tarsometatarsal kinematics was represented in the model as a hinge joint (i.e. a single instantaneous center of rotation throughout the range of motion). The bottom right panel shows the ranges of motion and kinematics for the iliosacral joint (flexion—extension of the vertebral column V relative to the pelvis; U, urostyle). The kinematics at this joint corresponded most closely to a gliding joint. The inset shows a diagram of the sacral diapophysis, which is the transverse process of the sacrum that forms a joint with the iliac process of the pelvis.