A 50-year-old lady presented With a 3-month history of pain in the lower third of the right thigh. There was no local swelling; tenderness was present on deep pressure. Plain X-rays showed an ill-defined intra medullary lesion with blotchy calcification at the lower end of the right femoral diaphysis,possible enchondroma or chondrosarcoma.Sections showed a cailaginous tumor.Which of the following histological features (if seen)would be most helpful to differentiate the two tumours?