The termination of thalamo-cortical fibres in the visual cortex of the cat.

An electron microscopic study has been made of the site and mode of termination of thalamo-cortical fibres in area 17 of the visual cortex of the cat. Thalamo-cortical fibres had been selectively interrupted 4-5 days before perfusion of the brain. In agreement with previous studies, degenerating axon terminals were found in layer I, in the deep part of layer III, and in layer IV of the cortex. In addition, a few degenerating thalamo-cortical axon terminals were found making synapses upon spines and small dendrites in layer VI. Two examples were seen of degenerating axon terminals making axo-dendritic synapses upon dendrites in continuity with their cell bodies. These neurons were not large stellate cells and were probably pyramidal.