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. Author manuscript; available in PMC: 2022 Jun 6.
Published in final edited form as: Nat Rev Neurosci. 2021 Oct 28;22(12):741–757. doi: 10.1038/s41583-021-00528-7

Fig. 2 |. Direct and indirect pathways from the cortex to the muscles.

Fig. 2 |

Traced axons (dots) from the primary motor cortex at the C8 level of the spinal cord. a | Such tracing has revealed that, in squirrel monkeys, neurons from the primary motor cortex (M1) project via the pyramidal tracts (blue region) to spinal interneurons (located in the yellow region), which in turn project to motor neurons (located in the red region). b | In capuchins, M1 sends direct projections to motor neurons in addition to indirect projections through spinal interneurons. Presumably owing in part to this direct pathway, capuchins are more dexterous than squirrel monkeys. CM, corticomotoneuronal. Adapted with permission from REF.204, Copyright 1993 Society for Neuroscience.