The relative size of Monodelphis domestica brains at P18, P35, P56, P180, P270-365, and >P365. The size and shape of the brain changes dramatically during the first six months of life. The caudolateral expansion of the cerebral cortex is particularly apparent. After sexual maturity (P180), there is little change in the size of the entire brain and the relative size of different structures. Images were converted to gray scale and contrast and brightness levels were adjusted using Adobe Photoshop. Scale = 2 mm.