l
bones, if the growth of one is arrested the continued growth of the
other results in a deviation of the hand or foot to one side.

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 an