Brain Development of 29 Day Old Embryo
The cerebral cortex--the most prominent feature when we think of a human brain--derives from the forebrain. This region is responsible for reason, planning, emotion, and problem solving, and by the end of the second trimester it is the primary visible structure. If you examine the surface of the cerebral cortex, you'll see convoluted folds; the raised surfaces are known as gyri and the "trenches" are sulci. These irregular folds provide greater surface area for cell-to-cell communication and interaction, increasing the brain's complexity.