The postnatal growth of the callosal connections of primary and secondary visual cortex in the rat.

The growth of callosal projections is completed earlier in primary than in secondary visual cortex. In area 17, the areal and laminar distributions of callosal projections are mature by days 9 and 12, respectively, whereas in area 18b, these developmental milestones occur by days 12 and 15, respectively. This suggests that the pruning and infiltration of callosal axons follow different schedules in different cortical areas.