REGENERATION AFTER EXARTICULATION 125 
in the stump in the former case. This cartilage becomes de- 
tached from the shaft, gradually breaks down and is, partly 
at least, reconverted into cartilage which assists in the formation 
of a new epiphysis. 
4. The new cartilage which forms the basis for the skeletal 
elements appears independently in three localities: 
a) Around the shaft of the bone proximal to the epiphysis 
(peripheral cartilage). This cartilage is periosteal in origin. 
b) In the axis of the bone and in contact with the marrow 
subsequent to detachment of the epiphysis (axial cartilage). 
The origin in this case is twofold: (1) From the cells of the old 
epiphyseal cartilage and (2) from the lining of the marrow cavity 
(endosteum). 
c) In the tissue of the bud distal to the epiphysis (embryonal 
cartilage). Here dedifferentiation appears to have taken place 
forming a substratum of indifferent cells from which in turn 
new cartilage is formed as in early development of the limb. 
5. If a single bone (fibula) is removed completely from the 
leg, it is not replaced either by proliferation from its fellow 
(lateral regeneration) or from the skeletal elements lying proximal 
and distal to it even when one of the latter is injured. 
6. When both leg bones are completely removed they are 
replaced to some extent by new elements which, however, are 
always irregular and incomplete. The origin of the new parts 
was not definitely determined. 
7. When one leg bone (fibula) and the foot are removed with- 
out injuring any of the remaining skeletal elements, a new 
complete foot is regenerated from the distal end of the remaining 
leg bone (tibia). This is followed by a slow and often incomplete 
regeneration of the lost leg bone (fibula) in a proximal direction 
(centripetal regeneration). 
