NAVICULA.E DISEASE. 



337 



placed tlian those of the fore limbs ? I thinl: the most devotsd 

 advocate of the theorj will scarcely venture to answer in the 

 affirmative; but shovild he feel inclined to think so, let him watch 

 a horse in motion with a load behind him, and he will very soon 

 see that the flexors of the hind limbs are called more powerfully 

 into action than those of the fore ones ; for in addition to actinf^ 

 as flexors of the feet and pasterns, they are extensors of the 

 hocks. If strain were the cause, navicular disease. owin<? to 

 the double function the flexor perforans is called upon to perform, 

 and the more powerful strain thrown xipon it in the removal 

 of heavy loads, would-be found in the hind, and not in the fore 

 feet. 



Flo. 59 represents the phalangeal bones in their naturally obliqna 

 position, and it will be seen that from the upper part of the 

 long pastern (o) bone, down to the too of the oa pedis (<•) is a con-i 

 tinuouB oblique line. TTua obliquity of position enables the bone to 

 act as a spring, for the purpose of modifying concussion. Every 

 horseman knows that the more oblique the pastern, the greater the 

 elasticity of step and freedom from jar ; that the pace is easy for the 

 horse, and delightful to the rider. The coronary bone (4) rests en- 

 tirely upon the oa pedis, and the navicular bene (c/) placed posteriorly 

 bears no weight, but gives increased leverage power to the tendon (f). 

 It is a mucoular appendage, like the sesamoida, and is not intended 

 to be a weight -supporting bone. 



Navicular di.sease is due to the rheumatoid diatlieais and to 

 coacussion, and the liability to suffer from the tirst-named 

 cause originates in hereditary prpdispo.sition and accidental 

 circumstances ; and to the second in conformation (as narrow 

 feet with short upright pasterns), and in the unnatural altera- 

 tion of the relative position of the navicular and weiglit-bearing 



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