Normal growth of the long bones proceeds from the ossification of cartilage cells in the epiphyses. At the zone of ossification the change from cartilage to bone takes place in an orderly manner; a columnar zone of calcification remains while new cartilage cells develop in the advancing zone. In this endochondral ossification the bone grows in length and at the same time "undergoes a remodeling process by which the new formed bone is pruned, reformed and incorporated as an intrinsic architectural part of the cylindrical shaft.1
This change from cartilage to bone may be interrupted by some inherent influence, and a partial or complete arrest of bone growth follows. Several well known clinical forms of defective development result from this interference, differing from each other to the extent that they have been described as separate clinical entities. These forms differ principally in the changes within the epiphyses, in the