Foetus at 27 weeks, sequence of coloured magnetic resonance imaging (MRI) scans. 16 scans run from left to right in four rows from top to bottom. All the scans pass through the uterus (brown), and are parallel sagittal foetal slices. That is, they are vertical side slices moving left to right across the foetus (yellow). The foetal head (lower left of the uterus) is at the base of the uterus. It appears first on the scans, and is followed by its body. The scan positions, chosen to allow study of the foetal brain, appear on three reference brain scans (bottom), of which one is frontal (coronal, right) and one is horizontal (axial, left).