ON THE NAVICULAll DISEASE. 11 



deviation from the natural position is not only obscr- Dis|,iaccnu>nt 

 vable on dissection, but is quite as apparent in the and coitiu bouW 

 living foot, by paring down to the quick those com- 

 missures or channels between the bars and frog 

 which will be found so morbidly deep, and take so 

 much time for the knife to reach the quick, that a 

 by-stander, ignorant of the nature of it, would be 

 induced to remark that such a horse was devoid of 

 blood in his foot. Exactly in proportion to this 

 morbid concavity externally is the morbid convexity 

 internally, and thus, with a fixed ascent of the frog, 

 an unnatural arch is formed : the soft elastic parts ^;j"^;;.'™.'^|^i^J 

 of the frog being absorbed, it becomes a rigid pro- °,Ie f^l'j;/''^''"' 

 tuberance, and is the rock of danger^, on ivhich I 

 am daring enough to assert that the most valuable 

 horses have struck. This protrusion of frog within 

 the foot is accompanied by an undue concavity of a hi^i.iy elastic 



. cushion de^e- 



sole and ri<>:idity of the bars. Ihe navicular bone neratcd into a 



~ _ rigid protube- 



lies transversely across this projecting part of therauce. 



frog, with the long flexor or perforans tendon pass- 



ino^ under, and, by articulating with the bone, The navicular 



.... . . joint, where si- 



forms the navicular joint. The joint receives its tuate. 

 share of the superincumbent weight from the small 

 pastern bone, and with violence, in the ratio of ra- 

 pidity with which the animal moves, and is re- 

 quired to yield and descend in proportion to the 

 impetus. It should also be remembered, that it is 

 placed immediately under the centre of weight, 

 which is conveyed in a perpendicular direction. 



