152 PBINCIPLES OP TETEBINAEY SUBGER7 



rail ; in trying to free itself the animal twists the incarcerated 

 hoof, resulting in fracture of the os corona, etc. 



Muscular action : Horses when cast in a narrow stall in 

 their vain efforts to rise strain the muscles of the back to the 

 utmost, executing at the same time all sorts of torsion move- 

 ments, resulting in fracture of the vertebral column. A very 

 similar thing is occasionally seen in the operating room; 

 horses when thrown for an operation will struggle violently 

 when lying on the bed, calling into most active play the 

 longissimus dorsi especially, as a result of which a fracture 

 of the dorsal or lumbar vertebrae is observed. Fracture of 

 the dorsal vertebrae has been seen to follow sudden rearing ; 

 that of the lumbar vertebrae in animals turning quickly and 

 short. Overtaxing the gastrocnemii or flexors of the knee 

 has been followed by fracture of the calcaneous and pisiform 

 bones respectively. 



Describe the predisposing causes. 



To this class belong the so-called idiopathic fractures. 

 In these fractures the bones seem possessed of abnormal 

 fragility ; a variety of fractures quite frequently seen in the 

 horse and cow, especially in certain localities, osteoporosis, 

 osteomalacia and tuberculosis apparently predisposing the 

 animals to fractures. Old animals are predisposed by reason 

 of senile atrophy, the very young by reason of their juvenile 

 bones ; those that have been ill and in the barn for a consider- 

 able length of time are predisposed by reason of inactivity 

 atrophy. 



Anchylosis of the vertebral column is another predispos- 

 ing factor. 



How are fractii/res classified ? 



1. Simple : there is no open wound leading to the break. 



