[United neurons in the cat motor cortex]

Vertically oriented bundles of apical dendrites in the cat motor cortex are described by means of light and electron microscopy. Existence of desmoidal and dendro-dendritic contacts in the bundles is considered as the structural basis of neuronal electrotonic interaction within the limits of one column. Sliding axo-spinal contacts are described between the descending pyramidal axon in layer III and the pyramidal apical dentrite in layer V which, probably, serve for the purpose of regulating activity of the main cortical output elements.