42 4 



Journal of Agrlcnliitrc. 



[8 July, 1907. 



its causation stands in needs of more elucidation in many aspects. 

 When affected with navicular disease the surface of the bone over 

 which the tendon plays becomes inflamed and ultimately affected with 

 caries or bone ulceration. The ulcers are often two in number, ooe 

 situated on each side of the middle line of the bone (,-Figs. 66 to 70). 

 Some authorities state that the disease commences in the tendon and ex- 

 tends to the bone and that the tendon becomes lacerated, but throughout 

 numerous ■post-mortem examinations the author has never seen this. He 

 consequently inclines to the view that the disease originates in the bone, 

 or in the pad of fibro-cartilage covering that surface of the bone over which 

 the tendon plays, and has as a cause, that concentration of pressure and 

 concussion at this particular spot which occurs in horses having a par- 

 ticular conformation of hoof and pastern — the narrow upright hoof and 

 vertical pastern. Horses with oblique pasterns seldom have navicular 

 disease and it practically never occurs in the hind feet where the concus- 

 sion is less but where the strain on the tendon is just as great as in the- 

 fore. Neither is navicular disease at all common where horses are not 

 used on hard roads. Although it is vet bv no means so common an 



Fig. 65. Inferior aspect of pedal and Fig. 66. Inferior aspect of pedal and' 



navicular bones showing tendon navicular bones with tendon drawn 



passing upwards over latter. (After back to show ulceration on navicular 



Hayes.) bone. (After Hayes.) 



affection as in England, it is a gradually increasing quantity in the cities 

 and towns of Australia. It was .seldom met with even among Melbourne- 

 horses until the early nineties. Its increase in the cities has been con- 

 current with the extension of wooden paving and macadamizing of the 

 thoroughfares. This observation strengthens the conclusion that, in 

 horses hereditarily predisposed to it bv particular conformation of hoof 

 and pastern, concussion plays the chiefest part in its causation. 



Excessive paring of the frog, by which, in shod horses, that anti-con- 

 cussive pad is prevented from contacting the ground, greatly increases the 

 jar on the navicular bone and is therefore a fertile contributory cause of 

 navicular disease. This practice of mutilating the frog — a practice which 

 is fortunately gaining disrepute amongst farriers— prevents the performance 

 of two of Its most important functions, viz. : — the lessening of concussive 



