Somite disintegration begins with the disruption and dispersion of cells in its ventromedial region, that upon detaching from the somite form a defined group of cells called “sclerotome”. The sclerotome is formed by scleroblasts that originate paraxial segments. Scleroblasts disperse and migrate forming the “sclerotomal mesenchyma”. This sclerotomal mesenchyma, in its evolution and cell differentiation, will give rise to skeletal tissues. One of the first features of the scleroblast is the production of extracellular matrix rich in hialuronic acid that facilitates the spreading of filopodia and the migration of the sclerotome. Sclerotome development is closely associated to the microenvironment created by the extracellular matrix in which scleroblasts are located. Hialuronic acid is found in the ample intercellular spaces occupied by the hydrated matrix.

White Leghorn chick embryos at H.H. stages 9 to 12 were fixed in 2.5% glutaraldehyde, postfixed in 1 % osmium tetroxide and embedded in araldite. Semithin transversal sections were stained with toluidine blue and visualized under the light microscope to locate the sclerotome.