SECTION XII 
THE SKELETON AND ITS JOINTS 
The bones with their articulations have been the 
subject of extensive study and research by zoologists in 
the direction, of classification and evolution. Adaptation 
of the osseous construction to the needs of the animal is 
well appreciated biological knowledge. For example, the 
keel of the sternum in birds affords broad origins for the 
flying muscles, the pectorals, which also insert on the 
alai of this bone and on the clavicle, and in addition use 
these latter formations as fulcra. So too the extremities 
of quadrupeds are angular in their upper two segments 
for the purpose of supplying a direct action of the flexors 
employed in running and leaping. The thick masseter 
muscle of carnivores is accommodated in the deep zygo- 
matic fossa. Many other examples might be cited, but 
these serve to direct attention to the adaptation of 
function and construction. Pathological changes in 
our materials are however too few to permit con- 
clusions as to possible relation of zoological position 
and development except such as may refer to deformity 
incident to the degenerative processes — rickets, osteo- 
malacia and osteogenesis imperfecta, and in these 
conditions the alterations are merely passive accommoda- 
tions to weakened support in order to obtain comfort. To 
put the matter in other words, it would seem that, aside 
from the diseases just named, there is no outstanding 
change in the skeletal tissues peculiar to zoological orders 
that might indicate vulnerability of the system or the 
methods of response to injury or disease. 
Effects of Trauma. 
There must be considerable reserve or reconstructive 
power in the bones of animals since it is a common thing 
at autopsy to see unmistakable evidences of repair of 
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