Corticomotoneuronal Organization

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Abstract
THE CORTICOFUGAL pyramidal cells, which are the "common paths"1 of cortical integration, are the key to the organization of the motor cortex (Msl of Woolsey2). They form the output channel of a complex input-output system, whose input side, as yet, has received less investigation than the output (for a review of recent work, see reference 3). This paper is concerned with one only of the outputs: the corticospinal neurons projecting monosynaptically to motoneurons innervating the baboon's arm, forearm, and hand. These constitute the simplest and most direct of the known corticofugal pathways. In the cat, which has no monosynaptic corticospinal projection,4 there are corticospinal projections controlling the interneurons of reflex arcs5 and the neurons and presynaptic arborizations of ascending spinal pathways,6 and it would be surprising if comparable projections did not exist in the primates. A projection to fusimotor neurons has been found in