The corpus callosum is one of the most prominent fiber systems of the mammalian brain. Early reports of animals in which the callosum was cut, often confused the effects attributable to callosum damage with those caused by lesions of other brain structures. Early clinical reports also failed to establish the role of the callosum in humans. Two sorts of evidence began to reveal the functions of the corpus callosum. People with callosal damage cannot read text presented in the left visual field, and animals in which the callosum is divided, and sensory input restricted to one hemisphere, fail to show interhemispheric transfer of learning. These functional findings are consistent with anatomical and physiological studies of the role of the corpus callosum in communication between the hemispheres.