Contribution to the morphometry of limb bud structures in the normodactylous and polydactylous rat. II. Density of filopodia in the subectodermal zone.

In hindlimb buds of normodactylous and polydactylous embryos in the stage of the 16th and 17th embryonal day the mesenchymal region, closely adjoining the site below the AER, was investigated. This space is called the subridge zone and is filled with a large amount of variously formed processes of mesenchymal cells, chiefly with filopodia. With the use of the morphometric point-couting method it was found that in normodactylous limb buds the density of filopodia in the given area of the subridge zone was 2.15% as compared with the 6.48% representation of filopodia in the same zone of polydactylous animals. Numerous filopodia localized right under the AER established connection between the mesenchyma and the intact basal membrane, and their higher density is undoubtedly related to the existence of the maintenance factor.