Any movement or isometric contraction is the result of the activation of many muscles. The selection and actual number of muscles participating in a movement are as widely varied as the movements themselves. Even when the same movement is repeated several times, no two repetitions are identical. The highest degree of freedom in the combination of muscles for synergistic or antagonistic action can be observed in the human hand and forearm. These muscles receive the most extensive innervation from the motor cortex. Whether this extensive cortical control is necessary for the achievement of such a large range of possible combinations of muscle action remains a question to which there is no direct answer, since no single experimental study has been devoted to the problem. Indirect evidence for such a functional organization comes from ablation studies, where lesions of the motor cortex lead to impairment of the most fractionated distal movements (159).