Morphometric analysis of osteoblast dynamics in the chick embryo tibia.

Structure and size of the osteoblasts have been analyzed during growth of the tibial diaphyses in chick embryos from 10 days incubation until hatching. Statistical analyses of the results indicate that both size and density of the osteoblasts gradually decrease from the subperiosteal towards the endosteal regions of the shaft; the osteoblast secretory territory, on the other hand increases. These structural changes of the osteoblasts, which appear to be related to differences of the appositional growth rate, seem to derive mainly from structural modifications of differentiated osteoblasts rather than from differentiation of new osteoblasts, of progressively smaller size, from osteoprogenitor cells. The data reported in this paper compared with those in previous investigations indicate that the size of the osteoblasts does not significantly differ in animals of different species.