ANATOMY AND PHYSIOLOGY OF THE HORSe’s FOOT. 187 
tendon and the surface of the navicular bone, to facilitate their 
movements on each other ; that this membrane is nearly, if not 
quite, as vascular and sensitive to injury as it is elsewhere ; and 
we have not far to seek for the true pathology of navicular- 
thritis. Disease, in some cases, may be confined for a long 
time to the synovial, or rather the fibrous, membrane covering 
this face of the bone, without the slightest change being 
perceptible in the spongy texture ; indeed, so dense is the 
compact tissue that, even in advanced stages of the malady, 
it yields but slowly to the disintegrating process, and thus 
protects the more vascular but less resisting cancellated 
structure, until it is itself destroyed. The rough ossific 
deposit we sometimes see on the surface of the navicular bone 
is due to the fibro-cartilaginous membrane.* 
With regard to the causes that induce this disease, it is 
not my intention to speak in this place ; it may be sufficient 
to state that, as an army veterinary surgeon, I have had 
opportunities for assuring myself that it can be produced in 
a moment in horses that have never worked onhard roads, but 
have been engaged in their first field days, and just dismissed 
the riding school, where they were trained on soft tan. 
Quite recently I saw it produced in a high-stepping mare 
during two days* severe exertion without preparation. 
What is termed concussion has little, if anything, to do with 
its production, as the navicular bone may be said to be better 
protected, or rather further removed, from this influence than 
any other bone in the fore-limb, perhaps excepting the 
supercarpal and sesamoid bones. If concussion caused any 
disease like this, far more likely would it affect the bones 
directly exposed, such as the pedal, coronary, or other bones 
immediately above these. 
The function of the navicular bone will be alluded to when 
we come to speak of the physiology of the horse's foot ; I 
have made this digression into its pathology more for the 
sake of showing how important a correct knowledge of 
anatomy is to the practitioner and pathologist than to 
venture to throw any new light upon a disease whose nature, 
* Less than twelve months ago I was obliged to recommend a mare to 
be destroyed, in consequence of incurable lameness, caused by disease of the 
long flexor muscle of the forearm, which became suddenly sprained on the 
picket-line some nine months previously. On examination, I found the bi- 
cipital grooves of the humerus, as well as the face of the flbro-cartilaginous 
tendon of the muscle that plays in these grooves, showing precisely the same 
morbid anatomy with which we are so familiar in navicularthritis, even to 
the most minute details. As is well known, this part of the humerus is, in 
its anatomical features, analogous to the navicular bone. 
