The growth of the human brain during the embryonic period proper. 1. Linear axes.

Linear axes of the brain were measured in 143 human embryos from Carnegie stages 11 to 23 (3 1/2-8 postovulatory weeks). The embryos ranged from 3 to 30 mm in C.-R. length. Both Born reconstructions and serial sections of the central nervous system were used. The brain axes included were the fronto-occipital diameter, bitemporal diameter, and length and width of both the mesencephalon and cerebellum. A least squares line was fitted to the set of data points corresponding to each brain axis measured, and a t test verified that a linear model was an appropriate representation of the data. Based on these linear measurements it can be concluded that for forebrain grows more rapidly than the rest of the brain at the onset of tubular brain enlargement. Furthermore, as seen by comparing growth along two dimensions, the forebrain and midbrain grow at the same rate, whereas the cerebellum grows at different rates along the length and height axes. In addition, the cerebellum begins to grow later than the rostral part of the brain. Covariance analysis of the data points of the embryonic brain axes with data points of identical brain axes of the fetus showed that the measurements from the embryonic and fetal brain axes cannot be represented by a single regression line.