638 
NAVICULAR DISEASE. 
is not the sole factor, but acts in conjunction with faulty trimming 
of the hoof. Williams’ view, that the most important factor is the 
failure to neutralise shock, appears incorrect, because under these 
circumstances the tendons would escape injury. Finally, it must not 
be forgotten that uprightness of the pastern may not only be a cause, 
but also a consequence of the disease. 
Peters explains the fact that horses which stand “over” on the front 
feet more often suffer from this disease, by drawing attention to the 
sharper angle made by the flexor pedis when passing over the navicular 
bone, and directs attention to the circumstance that when the limb is 
loaded, and the os pedis in consequence sinks, that tension in the 
tendons increases, and, consequently, that greater pressure is exercised 
on the os naviculare. 
The frequent occurrence of navicular disease in horses with long- 
pasterns is explained by the greater stress thrown on the tendons. On 
the other hand, obliquity of the pastern is in some respects an advan¬ 
tage, because the flexor perforans takes a straighter course over the 
navicular bone. 
Gunther thinks that turned-in toes predispose to the disease. Hert- 
wig’s view, that high heels favour its production, is based on a miscon¬ 
ception, though raising the frog from the ground may throw increased 
strain on the flexor tendons. The same applies to contraction of the 
foot, often blamed as a cause of the disease : it occurs during the 
development of the condition. 
Excessive pressure on the navicular bone accompanying sudden partial 
rupture of the perforans tendon may give rise to the disease, and was 
regarded by Fambach as the commonest cause. Moller inclines, however, 
more to Peters’ opinion, viz., that navicular disease is due to slowly- 
acting influences consequent on change in position between the bones 
of the limb or between them and the hoof axis, an idea which receives 
support from the slow character of the change. In riding and carriage 
horses, initial injury may be occasioned by sudden reining-in, jumping, 
continued sharp trotting, galloping, and occasionally even by slipping. 
English authors, among them Turner and Goodwin, think it may be 
caused by long rest, desiccation destroying the elasticity of the hoof and 
favouring the disease. Moller does not agree with Smith in thinking 
that continued standing on a particular foot causes the disease. He 
has often seen laminitis and descent of the os pedis under such con¬ 
ditions, but never navicular disease. Some of the above views may be 
due to faulty diagnosis and mistaking “contracted sole” for navicular 
disease, especially considering the favourable course noted by the older" 
English authors, who report 90 per cent, of recoveries. Bruises of the 
sole and frog are only occasional causes of navicular disease. 
