Excised specimen showing the periosteal lining (a), Photomicrograph showing tumour cells arranged in a biphasic pattern (H/E, ×40) (b), Photomicrograph showing light staining areas composed of plump myoid spindle cells arranged in short fascicles with elongated/cigar-shaped nuclei and dark staining areas composed of round or polygonal cells with slightly pleomorphic hyperchromic nuclei (H/E, ×100) (c).