542 
NAVICULARTHRITIS. 
that the farriers of old did not discover the hidden retreat of lame- 
ness ; but we have good reason to complain that veterinary colleges 
did not find out the seat of a lameness which was acknowledged 
by them as well as others to be in the foot. Had they cut into 
the navicular joint in any case where death happened to befall the 
lame horse, they could not have failed to have made the discovery; 
and the readiest way of laying open the joint for inspection is to 
make with a saw a vertical incision through the quarter of the hoof, 
on either side, carrying the incisions obliquely inward through the 
cartilages; then, with a scalpel detaching the perforans and per- 
forate tendons from their union with the contiguous parts, the 
former may be dissected down to its place of insertion, and turned 
back so as completely to expose the navicular (bursal) joint. 
The PARTS DISEASED, in cases of navicularthritis or grogginess, 
are the under surface of the navicular bone and the upper one of 
the perforans tendon. It will be remembered that the inferior or 
posterior surface of the navicular bone is covered with cartilage 
for the purpose of articulating, i. e. forming a bursa or joint with 
the opposed tendon of the perforans muscle, which in the motions 
of the bone, upward and downward, plays over it something after 
the manner of a rope over a pulley : the surfaces of the bone and 
tendon being in more complete co-aptation from the circumstance 
of the bone having a transverse eminence (or crest) across its 
middle, to which the tendon is fitted by a corresponding excavation 
in its substance, which hereabouts is rather of the nature of carti- 
lage than tendon. And both these cartilaginous surfaces being 
lined by a delicate vascular ( synovial ) membrane, the same as other 
bursal cavities are, which continually exudes joint-oil, the play of 
one upon the other is at once rendered facile and frictionless. 
Now, it is either the said crest across the navicular bone or 
the opposed concavity in the tendon, or both together, which shew 
the earliest signs of disease in cases of navicularthritis : of the 
two, Turner seems to give the priority to the tendon ; whereas 
Dr. Brauell informs us, his observations have proved to him 
that neither the navicular bone nor the bursa is the invariable 
nidus of incipient disease, “ it being as likely to arise in one tissue 
as the other;” and adds, “that when the bone is primitively 
attacked, the disease develops itself tardily and insensibly ; but 
that in the tendon the evolution of navicularthritis is comparatively 
rapid and decided.” Let which part will be first attacked, it is 
pretty evident that the opposed surface soon takes on the morbid 
action, either from direct contact, or, as Brauell says, from “ sym- 
pathy:” the curious accompanying fact being — one that casts a 
strong light upon the etiology of navicularthritis — that the upper 
or coffin-joint surface of the navicular bone, although covered with 
