The effects of paralysis on skeletal development in the chick embryo. II. Effects on histogenesis of the tibia.

In order to study the effects of paralysis on the development of bone, chick embryos were paralysed at 6 days of incubation and the pattern of histogenesis of the tibia was compared with that of control embryos by histology, scanning electron microscopy and morphometry. Up to 11 days of incubation the histological features of chondrification, initial perichondrial ossification and invasion by the vascular bud showed no differences. After this time the paralysed embryos exhibited a reduction in the formation of bone tissue and a reduced development of the fibular crest. The spread of cartilage resorption was also markedly reduced. In addition, scanning electron microscopy suggested a reduction in resorption of the innermost layers of bone. Blood vessels in the marrow cavity appeared smaller and those within developing osteones appeared larger than in the controls. In the paralysed embryos, morphometry confirmed a significant reduction in total volume of the tibia together with changes in its volumetric composition resulting from reduction in bone formation, cartilage formation and cartilage resorption.