[Experimental contribution to the formation of digital flexion creases]

Flexion creases on the toes of birds show remarkable similarities to human digital flexion creases, concerning both morphology and development. Muscle-free avian limbs were raised in the coelomic cavity or on the chorioallantoic membrane of chick embryos. Flexion creases were found to be formed after both procedures. From these experiments it may be concluded that regional differences, rather than mechanical factors, concerning the involved tissues are responsible for the formation of digital flexion creases. This may hold true also for human digital flexion creases.