1. Craniofacial Developmental Biology and Regeneration Branch, Craniofacial and Skeletal Diseases Branch, National Institute of Dental and Craniofacial Research, National Institutes of Health, Bethesda, Maryland 20892; Department of Orthopaedic Surgery, Osaka University Medical School, Suita 565-0871, Japan; and Department of Orthopaedic Surgery, Toyama Medical and Pharmaceutical University, Toyama