Comparative Light Microscopy. Light microscopic photomicrographs illustrate physeal/metaphyseal differences between cn/+ and cn/cn mice. a-c. Photomicrographs highlight the diminished hypertrophic zone of the physis in the cn/cn mouse (left) compared to the cn/+mouse (right) littermate. Images illustrate proximal humeral physes (a) at 2.5 weeks of age, distal femoral physes (b) at 3 weeks of age, and proximal tibial physes (c) at 5 weeks of age. The photomicrographs in the cn/cn mice also show a qualitative shortening of the proliferation zone of the physis even though the most prominent changes are in the hypertrophic zone. (×20, toluidine blue stain, marker = 50 μm). d. Photomicrograph shows prominent osteoclastic and vascular invasion activity at hypertrophic zone—metaphyseal junction in cn/cn mouse distal femur at 3 weeks. The vascular invasion however never advanced into the proliferating zone. (×40, toluidine blue stain, marker = 20 μm).