Observations on the Ossification of the Foot-Bones in Polydactyl and Normal Chicks

Publisher Website
Google Scholar
Abstract
Cleared and stained preps. of polydactyl and normal feet from chick embryos aged 6 1/2-19 days and from postnatal birds were studied. Ossification begins in the chick foot at about the end of the 7th day of incubation, and by the end of the 19th day has begun in all the long bones of the foot and the tarsalia. The order of ossification is not that of chondrification. No consistent bilateral variations in time of ossification were observed. Ossification begins earlier in [female] birds than in [male][male]. The normal chick embryo differs from the rat in the comparatively early beginning of ossification; from the guinea pig in the lack of ossification centers for sesamoid bones and for true epiphysial ossifications; and from the rat, guinea pig, and man in the order of ossification of the phalanges. Polydactylism in the chick is a condition of hyperphalangy of the hallux, manifested either as a lengthening or as a splitting of the digit. No definite order of ossification was observed in the phalanges of the polydactyl hallux. The evidence indicates that the extra toe in polydactyl birds is not an over-developed 5th toe.