THIS is the left cerebral hemisphere of an 18-month-old infant who lived some 800 years ago. Such finds are extremely rare, because nervous tissue is soft and normally begins to decompose soon after death, so this specimen is unique in that it has been far better preserved than any other. Although reduced by about 80% of its original weight, many of its anatomical features have remained intact. The frontal, temporal and occipital lobes have retained their original shape; the gyri and sulci (the grooves and furrows on the surface, respectively labelled G and S, above) are easily recognizable…