Longitudinal section through the distal end of a metatarsal bone of a 2-month-old infant. The epiphyseal (secondary) ossification center is well formed. Bone formation is taking place at both the epiphyseal and the diaphyseal surface of the epiphyseal plate. The zonation is apparent on the diaphyseal side because the growth rate there is so much greater than the epiphyseal ossification center. Because both centers are active, the zone of reserve cartilage is relatively narrow. H&E x280. (From Kelly DE, Wood RL, Enders AC. Bailey's Textbook of Microscopic Anatomy. Baltimore: Williams & Wilkins, 1978.)
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