In certain diseases, such as rickets and inherited syphilis, and in developmental anomalies such as achondroplasia, dwarfing of the skeleton results from defective growth of bone at the ossifying junctions.  Conversely, excessive growth of bone at the ossifying junctions results in abnormal height of the skeleton or giantism as a result, for example, of increased activity of the pituitary in adolescents, and in eunuchs who have been castrated in childhood or adolescence; in the latter, union of the epiphyses at the ends of the long bones is delayed beyond the usual period at which the skeleton attains maturity.

#Regeneration of Bone.#—­When bone has been lost or destroyed as a result of injury or disease, it is capable of being reproduced, the extent to which regeneration takes place varying under different conditions.  The chief part in the regeneration of bone is played by the osteoblasts in the adjacent marrow and in the deeper layer of the periosteum.  The shaft of a long bone may be reproduced after having been destroyed by disease or removed by operation.  The flat bones of the skull and the bones of the face, which are primarily developed in membrane, have little capacity of regeneration; hence, when bone has been lost or removed in these situations, there results a permanent defect.

Wounds or defects in articular cartilage are repaired by fibrous or osseous tissue derived from the subjacent cancellous spaces.

Transplantation of Bone—­Bone-grafting.—­Clinical experience is conclusive that a portion of bone which has been completely detached from its surroundings—­for example, a trephine circle, or a flap of bone detached with the saw, or the loose fragments in a compound fracture—­may become, if replaced in position, firmly and permanently incorporated with the surrounding bone.  Embedded foreign bodies, on the other hand, such as ivory pegs or decalcified bone, exhibit, on removal after a sufficient interval, evidence of having been eroded, in the shape of worm-eaten depressions and perforations, and do not become united or fused to the surrounding bone.  It follows from this that the implanting of living bone is to be preferred to the implanting of dead bone or of foreign material.  We believe that transplanted living bone when placed under favourable conditions survives and becomes incorporated with the bone with which it is in contact, and does not merely act as a scaffolding.  We believe also that the retention of the periosteum on the graft is not essential, but, by favouring the establishment of vascular connections, it contributes to the survival of the graft and the success of the transplantation.  Macewen maintains that bone grafts “take” better if broken up into small fragments; we regard this as unnecessary.  Bone grafts yield better functional results when they are immovably fixed to the adjacent bone by suture, pegs, or plates.  As in all grafting procedures, asepsis is essential.