Contribution to the morphometry of limb bud structures in the normodactylous and polydactylous rat. I. Apical ectodermal ridge.

The height of the apical ectodermal ridge on limb buds of the embryo laboratory rat was studied in the polydactyly-luxate syndrome and compared with the controls. The following findings were obtained: (a) On the 14th embryonal day, prior to the development of the anlage of mesenchymal condensates, the AER is higher in polydactylous animals as compared with the controls. (b) On the 15th, 16th and 17th embryonal day the height of the AER in the praeaxial region of the polydactylous limb bud largely predominates over the controls. A comparison of the height of the AER above digital rays and interdigital grooves of polydactylous and normodactylous animals does not thus exhibit any marked differences. This fact is attributed to the existence of more powerful induction processes of the underlying mesenchymal component where rudiments of supernumerary digital rays are formed.