The differences of fractures depend upon what bone is broken, what portion of it is fractured, the direction of the fracture, the respective position of the fragments, and lastly, upon circumstances accompanying the injury and making it simple, compound, or variously complicated.

Firstly, then, with respect to the bone affected. Sometimes it is one of the broad bones, such as the scapula or shoulder-blade, etc, sometimes it is a short bone; but far more commonly it is one of the long bones. The situation and functions of the broad bones render their fractures un-frequent.

Then, again, fractures of the short bones are still more unusual, because these bones, being nearly equal in their three dimensions, are capable of greater resistance, and are not often within the reach of external violence. Besides, most of them are little exposed to the operation of outward force by their situation of function. Hence, except when a paw is crushed, accidents to them are rare. But the long bones which serve as pillars of support to the dog are from the very nature of their functions particularly liable to fracture.

Secondly, with respect to the part of the bone broken. The long bones may be fractured at different points. Very often their middle portion is broken, and in this circumstance they generally break like a stick which has been bent beyond its extensibility by a force applied at each end of it. Sometimes the fracture occurs more or less near the extremities of the bone, which is always a very undesirable event. Lastly, the bone is sometimes broken in several places, and the injury may be produced by two different causes which operate successively, or simultaneously, upon the broken parts of the bone, or it may be occasioned by one single cause which acts at the same moment upon several points of it. Now these distinctions of fractures, be it remembered, are not mere scholastic refinements; they have a truly important influence over the prognosis and treatment of the case.

Thirdly, with respect to the direction in which the bone is broken. Thus fractures are distinguished into transverse and oblique. The obliquity renders the surface of the injury larger, and materially increases the difficulty of maintaining the ends of the bone in contact after the fracture has been set. Oblique fractures are subject to considerable variety, which depends upon the degree of their obliquity, and whether they are partly oblique and partly transverse.

When a bone is broken in different places at once and divided into several fragments or splinters, the fracture is termed comminuted.

Fourthly, with regard to the respective position of the fragments. These differences are highly important, because the treatment essentially consists in obviating or preventing the displacement of the fragments. It is not, however, to be supposed that such displacement is a constant effect of all fractures, for it seldom takes place where there are two bones and only one of them broken. But when both bones are broken there is generally more or less displacement, and such is always the case where we have one of the long pillars broken.

Again, the displacement may happen in respect to the diameter, length, direction, or circumference of the bone.

With respect to the length. The mode of displacement in which the ends of the broken bone pass more or less over each other is chiefly noticed in oblique fractures, but sometimes in transverse ones, when the displacement in the direction of the diameter of the bone has been such that the surfaces of the fracture are no longer in contact. So whenever the limb is shortened, it is by displacement of the lower fragment.

With respect to the causes of displacement I may remark, that as the bones are only passive instruments of locomotion, they do not possess in their own organisation any power capable of causing the change of situation which takes place, but yield to the impulse of external bodies, the weight of the limb or part, and the action of the muscles.

The displacement may be produced by an external force, either at the moment when the fracture happens, and by the very action of the same cause as breaks the bone, or it may be caused by the weight of the body when the fracture precedes the fall, or lastly, it may be brought on by some other external force, acting on the fragments sooner or later after the occurrence of the injury.

The outward violence operates sometimes directly on the situation of the fracture, sometimes on parts more or less distant from it. In both cases, then, the action of the force is not confined to the production of the fracture, but is partly spent in causing a displacement of the fragments.

Again, the weight of the limb itself may produce displacement, according to the direction or circumference of the bone, as already detailed. The disturbance of the limb by the patient may sometimes alter the relative situation of the fragments and thus cause displacement.

But of all the causes of the displacement of fractures, the action of the muscles must always be taken into consideration; because amongst the muscles surrounding a fractured bone soma are attached to it throughout its whole length and are equally connected with both fragments. Some arise from the bone above, and are inserted either into that which is articulated with the lower fragment or into the lower fragment itself. Lastly, others come from a point more or less distant, and terminate in the upper fragment.

Now, the muscles attached to both fragments perhaps contribute but little to the displacement. Still they may, however, draw them to the side on which they are situated, and thus change the direction of the limb. A most unfortunate sequel, especially if the dog is a valuable one.

Fifthly, with respect to circumstances with which fractures are accompanied. The most important division of fractures is into simple and Compound.

By a simple fracture is meant a suddenly formed breach in the continuity of one or more bones, without any external wound, communicating internally with the fracture.

By a compound fracture is meant to signify the same sort of injury of a bone, or bones, with the following addition. That is, it is attended with a laceration of the integuments, which laceration may be produced by the protrusion of one or both ends of the fracture through the skin, or by a ball or other body which enters or otherwise wounds the soft parts, at the same moment that it breaks the bone.

Fractures are said to be complicated when' they are attended with disease or accidents, which render the indications in the treatment more numerous, and require the employment of different remedies or the practice of sundry operations for the accomplishment of the cure.

Thus fractures may he complicated with severe degrees of contusion, wounds of the soft parts, injury of bloodvessels, a dislocation, or diseases and particular states of the constitution - for example, rickets, cancer, or pregnancy in bitches, etc.