In rhesus monkeys (Macaca mulatta), ablation of the premotor and supplementary motor areas and the adjoining rostral half of the precentral gyrus impairs the capacity of the contralateral arm to reach around a transparent obstacle to a visible food reward, and results in a tendency of this arm to reach around a transparent obstacle to a visible food reward, and results in a tendency of this arm to reach straight to where the food is visible. This may reflect a disinhibition of brainstem pathways which steer the arm and hand straight ot a visual target.