338 



DISEASES OF THE FEET. 



bones, brought about by the application of shoes which are 

 either turned down, calkined, or made thicker at the heels 

 than at the toes. 



'3/ 



■■. c 



Fig. 60 represents the bones when their position is altered by a 

 thick -heeled shoe ; the line is changed from its natural obliquity to a 

 direction approaching the perpendicular. The lower end of the os 

 coronse (b) is made to rest upon the navicular {d), as well as iipon the 

 pedal bone (c). The navicular bone is made to bear weight for which 

 it was not intended, neither is its structiire calculated to do so. All 

 weight -bearing bones have their fibres arranged to receive weight 

 upon their extremities, but the fibres of the navicular, and of all the 

 sesamoidean bones or muscular appendages, are not so arranged, and 

 weight thrown upon them induces disease. 



The development of navicular lameness from rheumatoid 

 disease is occasionally due to what Professor Dick termed 

 " occasional exercise," which implies long periods of rest, inac- 

 tivity, and irregular work. Professor Dick maintained that 

 during rest there was a deficiency of synovial secretion, and 

 that when an animal, with his joints and bursas in this dry 

 condition, was suddenly put to fast work, the effects of the 

 friction upon the surface of tendon, moving under the bone, 

 were laceration of its fibres and navicular disease. Whether 



