The arrangement of collagene fibers in bone epiphyses and mataphyses form various species of reptiles and mammals was studied with a polarized light microscope and with a scanning electron microscope. In spite of the variety of shape observed in the long bone extremities of different species, the collagenic fibers arrangement in the bone epiphyses and metaphyses appeared constant. Even in reptiles known to lack a growth plate, the metaphyseal and epiphyseal fiber patterns evoked those observed in mammals. A common fiber pattern may therefore be proposed which allows the coexistence of two apparently incompatible functions: growth, that induces an increased fragility at the epiphyseo-metaphyseal junction as opposed to mechanical support, which has to cope with load and traction forces at the same junctional site.