Staging of the early embryonic brain in the baboon (Papio cynocephalus) and rhesus monkey (Macaca mulatta)

Early morphogenesis of the brain and its derivatives was studied in sixty-nine baboon and rhesus monkey embryos representing developmental stages 8-16, and compared with the staged human embryo. The baboon and rhesus monkey embryos develop in a similar temporal sequence when compared with human embryos with the following exceptions: 1) The respective developmental events for otic disc, adenohypophyseal pouch, and hippocampal internal sulcus formation in the baboon and rhesus monkey occur at stage 10, stages 11-12, and after stage 16, while the comparable stages in humans are 9, 10, and 16; 2) Alternatively, formation of the trigeminal primordium and the motor root of the trigeminal nerve and evagination of the neurohypophysis occur earlier in the baboon and rhesus monkey (i.e., stages 12-13, stage 14, and stage 15, respectively) than observed in the human embryo (stage 14, stage 15, and stage 16, respectively); and 3) Lens pore closure in baboon and human embryos takes place during stage 14, while in the rhesus monkey closure occurs during stage 15.