The Bulletin 
7 
The walls of the medullary spaces are of considerable thickness at this 
time, but they become thickened by the deposit of layers of new bone in 
their interior in the following manner: 
Some of the osteoblasts arrange themselves as an epithelioid layer 
on the surface of the wall of the canal. This forms a bony stratum 
and thus the space becomes gradually covered with a layer of true 
osseous substance. By the repetition of this process the original cavity 
becomes very much reduced in size, and at last remains a small circular 
hole, containing blood vessels and a few osteoblasts. This small cavity 
constitutes the haversian canal of the perfectly ossified bone. These 
canals are essential in the regeneration of bone. 
Other changes may be observed at the centers of ossification. A 
similar process has been set up elsewhere and has been gradually pro¬ 
ceeding toward the end of the shaft, so that in the ossifying bone all the 
changes described above may be seen in different stages, from the true 
bone in the center of the shaft to the hyaline cartilage at the extremity. 
II. The Beparative Processes of Bone 
Fracture of Bones 
A fracture may be defined as a sudden dissolution of continuity in a 
bone. The causes of these in a fowl are: 
First, injury or trauma, as may be caused by a blow from a stone or 
stick or by being stepped upon by a large animal such as a horse or cow, 
or by a gunshot wound. 
Second, muscular action. The effect of this can be seen when it is 
known that bones are most resistant first to traction, next to pressure, 
still less resistant to flexion or bending, and least of all to torsion. 
External violence may be direct or indirect. In fracture from direct 
violence the bone is broken at or near the spot where the violence is 
applied. As a rule, the soft structures surrounding the fracture are 
more or less injured, and more serious results may follow than in frac¬ 
tures by indirect violence. In fractures caused by this direct violence 
the bone may be comminuted or fissured and perhaps driven into vital 
organs, as the liver or lungs, if the fracture be near those regions, or into 
the brain if it be near the cranial region. 
In indirect violence the fracture occurs at a distance from the spot 
where the violence is applied. The bone usually breaks at its weakest 
point. The fracture may be rendered compound from the fragments, 
which often are much displaced and are sharp and irregular, being 
driven through the soft parts. 
External violence is the most common cause of fracture in the fowl. 
The most common bones that are fractured by this cause are those of the 
legs, and, next, those of the wings. 
