The characteristic features of this dystrophy are, in the infantile form, the failure for most of the ossification to pass beyond the stage of calcification, and the presence of multiple fractures; in the infant, multiple fractures, flattened vertebral bodies, expanded extremities of the tubular bones with a relative hypoplasia of the shaft, tendency to ballooning of a thin skull. Towards puberty, marked irregularity in growth in the metaphyseal borders of the epiphysis and expanded ends of the diaphyses, suggesting proliferation of cartilage, osteoid or other pre-osseous tissue instead of bone. In the adolescent and adult, localised thinning and bulging of the skull, marked deformities of the ribs and pelvis. Slender shafts of the tubular bones of the lower extremity, composed chiefly of compact cortical tissue with extremities which are expanded to almost normal size, but made up of an open cancellous structure which makes them relatively radio-transparent. Marked bending of the pelvis and bones of the lower extremity indicate an unusual degree of plasticity.