. Bulletin of the Natural History Museum Zoology. Fig. 14 Views of specialised climbing lacertid ascending vertical surface; a, b dorsal; c. d lateral. Crus and foot are not extended far forwards and hind digits flex mesially at end of power stroke, the body is kept very close to the surface being climbed. Many lacertids climb on open continuous surfaces such as rocks and tree boles and branches. These vary in steepness, from gentle slopes to vertical and even overhanging surfaces, and lizards may run directly up them, or descend, or travel laterally or obliquely. Locomotion in specialised lac
. Bulletin of the Natural History Museum Zoology. Fig. 14 Views of specialised climbing lacertid ascending vertical surface; a, b dorsal; c. d lateral. Crus and foot are not extended far forwards and hind digits flex mesially at end of power stroke, the body is kept very close to the surface being climbed. Many lacertids climb on open continuous surfaces such as rocks and tree boles and branches. These vary in steepness, from gentle slopes to vertical and even overhanging surfaces, and lizards may run directly up them, or descend, or travel laterally or obliquely. Locomotion in specialised lacertid climbers often has many simi- larities to that of ground dwellers, but there are marked differences, especially when ascending perpendicular and near-vertical faces. In this situation, a lizard like Lacerta oxycephala climbs with its body very close to the surface and the limbs spread laterally so the distal extremity of the femur does not pass dorsal to the crus during the power stroke (Fig. 14). As in ground dwellers, the limbs work in diagonal pairs. Each hind foot is placed lateral and posterior to the ipsilateral forefoot and the hind leg in each diagonal limb pair is delayed relative to the foreleg so that, as the recovery phase is brief, the proportion of time when two feet are out of contact with the substratum is small. In observed sequences of climbing in Lacerta oxycephala, the recovery phase took between an eighth and a quarter as long as the power phase, the smaller proportion being during slow climbing. Counts of the number of frames of cine film in which four, three and two feet gripped the rock suggest that four legs may be in contact for over half, and three legs for over three-quarters of the total time; there is consequently no floating phase. This pattern contrasts strongly with fast locomotion in specialised ground dwellers where two legs are usually out of contact with the substratum and sometimes all four. The distance between the consecutive foot h
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