A 14-year-old girl from rural Maharashtra presents with a 4-month history of pain and swelling in the right tibia. She reports night sweats and has lost 3 kg in weight. On examination, there is a firm, tender swelling over the proximal tibia with warmth and restricted knee movement. Laboratory findings: hemoglobin 10.2 g/dL, ESR 92 mm/hr, alkaline phosphatase 180 IU/L. Plain radiographs show a mixed lytic and sclerotic lesion in the diaphysis with periosteal new bone formation. A biopsy is performed. Which of the following histological findings would be most consistent with the suspected diagnosis?