THE ULNA 51 



joint, such as results from slipping forwards with the solar aspect of the 

 fore-feet fiat on the ground. It will be readily understood that in such 

 cases the angle formed by the long axes of the radius and humerus 

 becomes suddenly and greatly increased, and causes great pressure to be 

 thrown on the olecranon process by the floor of the olecranon fossa, with 

 the result that the former snaps off. The summit of the olecranon 

 process gives attachment to the tendon of the triceps extensor cubiti 

 muscle, and we now have inability of this muscle, which becomes sud- 

 denly relaxed, giving us symptoms very much resembling those of radial 

 or musculo-spiral paralysis. The caput magnum, which, as we have 

 already stated, takes a great part in suspending the humerus at its 

 normal angle with the scapula, is now relaxed, with the result that 

 the distal end of this bone is let down, and we have " dropping " of 

 the elbow. 



The condition is readily diagnosed, but unfortunately treatment is 

 almost useless to restore the part to its pristine condition. This is due to 

 the fact that the fracture usually passes through the articular surface of 

 the sigmoid cavity, and also to the extreme difficulty experienced in main- 

 taining the surfaces of the fractured pieces in apposition, owing to the 

 traction exerted upon the olecranon process by the triceps muscle. For the 

 latter reason it is stated that in the human subject the fractured olecranon 

 usually unites with the body of the bone by means of fibrous tissue — i.e., 

 a false joint is formed. When this occurs in the horse the animal remains 

 permanently lame. 



When the fracture occurs low down the ulna, a plaster bandage is 

 sometimes applied to the limb from the knee to the elbow, and the animal 

 placed in slings. By these means the radius is utilised as a splint to keep 

 the ulna in position. Bourgelat's splint is occasionally utilised. But in 

 this method the difficulty is to overcome the retarding effisct of contraction 

 of the triceps, a difficulty which is much greater in the horse than in 

 animals in which the ulna is so much better developed, such as the dog 

 and ox. 



