The most direct effect of severing the corpus callosum would be that

The most direct effect of severing the corpus callosum would be that the cerebral hemispheres could not directly communicate, since the corpus callosum is the set of nerve fibers that unites both cerebral hemispheres, this structure is located in the midline of the brain, situating itself in the interhemispheric fissure and being mostly hidden from external observation when it is partially obscured by the Cortex.

Then it is june the conclusion to the second sentence is just restating "if it is june then it is summer"