Cytoplasmic modifications at the contact zone of osteoclasts and calcified tissue in the diaphyseal growing plate of foetal guinea-pig tibia

Longitudinal sections of foetal guinea-pig tibia prepared from decalcified and undecalcified samples were examined in the electron microscope. Osteoclasts in contact with calcified tissue in the growing plate of the diaphysis showed a modified oval-shaped cytoplasmic zone, situated at the brim of the cup-like depression containing the ruffled border, with dense material arranged either in parallel bands or in a loose network according to the section observed. This modified zone, interpreted as roughly ring-shaped around the edge of the resorption region, probably participates in the development of the ruffled border and thus contributes to the extension of the surface of active resorption.