204 DISEASES OF THE JOINTS. 



the horse uneasy to its rider, and destroying that motion of 

 adaptability wliich is pre-eminently characteristic of that ani- 

 mal, and which enables it to perform an amount of speed with 

 a weight upon the back that would, without this provision, be 

 sufficient to cause by its concussion such injury to its internal 

 economy as to produce disease, and even death. 



Causes. — This disease is generally produced by the animal 

 being compelled to bear a weight disproportionate to its 

 strength. In some cases, however, it proceeds from no external 

 appreciable cause ; it must therefore arise from a constitutional 

 diathesis; the bones becoming fragile, fatty, and degenerate 

 in condition, liable to fracture from trivial causes, such as the 

 moderate contraction of the muscles attached to them, or even 

 to be spontaneously broken. (See Photo-lithograph, Plate IV., 

 Fig.l.) 



The specimen from which this plate is taken beautifully 

 illustrates this peculiar pathological condition. When newly 

 prepared, and up to the present time, it is found to resemble, in 

 its external appearance, an old fossil bone of a dirty rusty-brown 

 colour, greasy to the touch, and crumbling under moderate pres- 

 sure. Microscopically examined, it presented numerous oil 

 globules, its bone corpuscles much altered in shape, and in 

 many of their special characteristics. It will be seen that an 

 old-standing fracture exists, and that a process of repair, repre- 

 sented by the enlargement, with a fissure running through its 

 whole thickness, had gone on to a considerable extent. The 

 animal from which the specimen was taken presented no symp- 

 toms of having its back in this condition, nor of the fracture 

 during life. He was a very old pony, and was accidentally 

 bought for dissection. The whole of his spinal column, from 

 the sacrum to the middle of tlie cervical region, was more or less 

 affected ; the anchylosis being complete between all the lumbar 

 and dorsal vertebrae, but only in the rudimentary state in those 

 of the cervical region. Had this animal been cast for an opera- 

 tion, the result would inevitably have been a broken back, no 

 matter how carefully such casting had been performed. Veteri- 

 narians will bear this in mind, and are here exhorted to make a 

 careful 2^ost mortem examination of every case of such an acci- 

 dent, not only as to the mere presence of the fracture, but into 

 the pathological condition of the bones. 



