The earliest workers in bone were concerned with its resorption. Howship, 1 in 1815 and 1817, discussed physiologic and pathologic resorption, but others before him had already called attention to this subject. Later, Koelliker, 2 using the newer methods of histologic technic, applied himself especially to a study of physiologic resorption and recognized the importance in this process of the multinucleated giant cell, which he called osteoclast (bone breaker). Many of his conclusions in regard to the osteoclast have been applied in their entirety to patholigic resorption, with the consequent neglect of other factors which play a part in such resorption. Even physiologic resorption is not brought about solely by osteoclasts. Physiologic resorption was recognized many decades ago as important in the development of the skeleton, which is reconstructed several times before it reaches its adult form. Physiologic resorption can be studied when the cartilaginous skeleton is removed and replaced