The cerebellar cortex of the chicken embryo contains parasagittal segments of Purkinje cells. At intermediate stages of development, cell-dense ribbons of migrating granule cells ("raphes") are found between the segments. The complementary pattern of granule cell raphes and Purkinje cell segments represents a basic scheme of cerebellar organization that coincides with the expression domains of various genes, such as cadherins, gene regulatory proteins, and ephrins and their receptors. We have recently found the raphe/segment pattern also in a mammalian species, the postnatal mouse. Like in the chicken, the parasagittal raphes of granule cells were observed at the boundaries of Purkinje cell segments that differentially express cadherins. The number and arrangement of the raphes in the different cerebellar lobules is roughly similar in both species. The raphe/segment pattern is thus more widely distributed in vertebrates than previously assumed.