periods. In the first they are surrounded
by an external bony ring, and the medullary cavity is closed by a bony
plug or stopper, constituting the period of the provisional callus. This
is followed by the period of permanent callus, during which the process
of converting the cartilaginous into the osseous form is going forward.

The restorative process is sooner completed in the carnivorous than in
the herbivorous tribes. In the former the temporary callus may attain
sufficient fineness of consistency for the careful use of the limb
within four weeks, but with the latter a period of from six weeks to two
months is not too long to allow before removing the supporting apparatus
from the limb.

This, in general terms, represents the fact when the resources of nature
have not been thwarted by untoward accidents, such as a want of vigor in
the constitution of the patient or a lack of skill on the part of the
practitioner, and especially when, from any cause, the bony fragments
have not been kept in a state of perfect immobility and the constant
friction has prevented the osseous union of the two portions. Failures
and misfortunes are always more than possible, and instead of a solid
and practicable bony union the sequel of the accident is sometimes a
false joint, composed of mere flexible cartilage, a poor pseudarthrosis.
The explanation of this appears to be that, first, the sharp edges of
the ends of the bone disappear by becoming rounded at their extremities
by friction and polishing against each other. Then follows an exudation
of a plastic nature which becomes transformed into a cartilaginous layer
of a rough, articular aspect. In this bony nuclei soon appear, and the
lymph secreted between the segments thus transformed, instead of
becoming truly ossified, is changed into a sort of fibrocartilaginous
pouch, or capsular sac, in which a somewhat albuminous secretion, or
pseudo-synovia, permits the movement to take place. Most commonly,
however, in our animals, the union of the bony fragments is obtained
wholly through the medium of a layer of fibrous tissue, and it is
because the union has been accomplished by a ligamentous formation only
that motion becomes practicable.

_Prognosis._--The prognosis in a case of fracture in an animal is one of
the gravest vital import to the patient, and therefore of serious
pecuniary concern to his owner. The period has not long elapsed when to
have received such a hurt was quite equiv