224 HEALTH AND DISEASE 



are liable to be torn away by muscular contraction, or otherwise forcibly 

 displaced. 



Structural alterations, the result of disease, by weakening the bone 

 tissue, lessen its power of resistance to ordinary forces, and thereby con- 

 duce to fracture. 



The navicular bone, after a period of ulceration, breaks beneath the 

 weight thrown upon it in action. 



The imperfectly - developed bones of the rickety foal, after bending 

 under the strain imposed upon them, may sooner or later present a partial 

 or complete fracture. 



Various other morbid changes, such as cancer, osteo-porosis, melanosis, 

 &c., render bones specially amenable in this direction to causes which they 

 would otherwise resist. 



Season of the year, and the nature of the surface over which horses 

 travel, tend to increase the liability or predispose to fracture. 



In winter, when the roads are covered with ice, and in towns where 

 horses have to travel over wood pavement or other smooth surfaces made 

 slippery with water, legs, hips, and ribs are in consequence frequently 

 broken. 



The exciting causes of fracture are : 1 , external violence, such as kicks, 

 collisions, falls, blows, twists, &c. ; and 2, muscular contraction. 



Violence may operate either directly or indirectly, i.e. it may break 

 the bone to which it is immediately applied, or some other at a distance 

 from it. It sometimes occurs that a horse felling ui^on the poll, and 

 striking the occipital bone, breaks the sphenoid bone at the base of the 

 brain. Horses fracture the os suffraginis, or long pastern, or even the 

 canon-bone by pitching on the toe while endeavouring to save themselves 

 from a fall, or in jumping or galloping. 



Examples of fracture as the eftect of muscular contraction are seen 

 in those common accidents which occur to horses while being cast, or in 

 the course of a surgical operation. The violent struggles to free them- 

 selves from restraint too commonly give rise to a broken back, or a broken 

 thigh, or the breaking away of one of the epiphyses or bony projections 

 from the shaft of a bone. 



Symptoms. — To determine the presence of a fracture in the horse is 

 sometimes a very difficult, and may be an impossible task. The parts to 

 be dealt with are large, heavy, and do not lend themselves to that thorough 

 and searching examination which is so capable of being made in the smaller 

 animals. Besides, the excitable and refractory character of the horse 

 greatly interferes with that full control so necessary to a successful 

 diagnosis. Of course we can brino- to our aid the restraining influence of 



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