Electron microscope study of osteoclasts with special reference to the three-dimensional structure of the ruffled border.

Osteoclasts of rat mandibulars were observed under the transmission electron microscope with the aim of understanding the three-dimensional structure of the ruffled border. After observation, the same block was remounted to obtain sections of the same osteoclasts at right angles to the first sectioning plane. The structure of the ruffled border of osteoclasts was observed in the two perpendicular directions. The ruffled border of osteoclasts was found to consist of two areas: one being composed of finger-like processes and the other, of plate-like processes. The distribution of the two areas of processes in the ruffled border did not show any apparent regularity. Not all processes continued to the cell body; some processes (stem processes) did while others were interwoven branches of the stem processes. The finger-like processes were long and rod-shaped and a few of them branched directly from the stem processes. The plate-like processes were long and belt-like and showed complicated branching from the stem processes; some of these were possibly the long belt-like processes that were complicatedly folded up to make many secondary plates; they are arranged parallel to each other in a given area. The relationship between the structure and function of the ruffled border is discussed.