36 Williams, Fisher, and Udall. The Spavin Group. 
second and third phalanges above and in front, and the tightly 
stretched flexor pedis tendon behind and below. The com- 
pression may be varied somewhat on the superior surface and 
shifted from one articular facet to the other by changing the 
relation of the coronal and pedal bones, but, so long as weight 
is borne, the pressure on the inferior or tendonous surface is 
constant and unchangeable. The superior surface of the bone 
remains apparently normal as a rule, while the inferior face 
undergoes serious changes -in which the tendon also shares. 
The anatomical relation of the navicular bone is alike in front 
and behind, but a horse bears approximately fifty-five per cent. 
of his weight upon his anterior limbs, and the burden is so great 
that normally both feet share it constantly in the same degree, 
while in the hind feet the weight-bearing demand, when stand- 
ing, is unimportant and the limbs are alternately rested. The 
anterior navicular bones suffer often and severely, those of the 
posterior limbs almus. never. Some say that strain or concus- 
sion plays the greater rdle here, but the strain is certainly 
greater during locomotion in the hind than the fore foot, and 
the concussion is far less in the navicular than in other neigh- 
boring bones. 
In ringbone the occurrence of the affection most frequently 
in front is again quite as suggestive of compression as of con- 
cussion or strain, though admittedly the two latter play a far 
greater role here than in navicular disease. 
In spavin we find the disease affecting with greatest fre- 
quency those bones which are under the most constant com- 
pression. The tendo-achilles behind, the flexor metatarsi in 
front, by their tension when the foot is at rest permit little 
relief from the compression of the cuneiform bones between 
the head of the metatarsus and the astragalus. When weight. 
is placed upon the limb, the compression of these bones con- 
tinues. To add to this, acute pressure is brought to bear upon 
the seat of spavin by the crossing over it of the tightly stretched 
cunean tendon. The theory of Dieckerhoff, allotting to this 
stretched tendon an important réle in the causation of spavin, 
though we regard it as secondary, is in our judgment thoroughly 
justified, and the relief from spavin lameness secured by cunean 
tenotomy adds weight to the theory. 
The belief in the importance of compression is further sup- 
ported by the alleviation of spavin, ringbone, and especially 
