Invariance of the relative positions of structures attached to long bones during growth: cross-sectional and longitudinal studies.

This article reports the results of cross-sectional and longitudinal studies on the positions of muscles relative to bones. The cross-sectional study reports on the positions of 20 muscles attached to long bones in the chicken from prehatching ages to maturity. The results show that these muscles maintain constant positional relationships during growth as was reported in an earlier study by the authors using rabbits. The longitudinal study reports on the migration of the semitendinosus muscle in the rabbit during growth. The results show that this muscle migrates the distance predicted by the regression equations derived from the cross-sectional study. These results are related to the model of the periosteum as an expanding elastic sleeve attached at its ends to the epiphyses and put under tension by the activity of the epiphyseal plates. In this model the soft structures attached to bones are seen as attached only to the periosteum in growing animals and thus carried along as hitchhikers by the expanding periosteum.