ANATOMY AND PHYSIOLOGY OF THE HORSE’S FOOT. 359 
of blood-vessels, more particularly on the surfaces of contact, 
than is observable elsewhere. For instance, the fibrous and 
synovial membrane covering the posterior gliding surface 
of the coronary bone is supplied with a very rich plexus 
throughout its superficies, while the face of the tendon that 
comes into contact with it is also highly endowed in this 
respect. With the capsule in question, however, this general 
distribution of blood-vessels is not observed, though both 
opposing surfaces appear to be covered by synovial mem- 
brane. At the upper and lower borders of this face of the 
navicular bone loops of vessels advance beneath the synovial 
membrane as far as the actual gliding surface, and there stop ; 
and this part presents a smooth, pearly, or yellowish-white, 
fibrous appearance. On the corresponding portion of the 
tendon the same features are noticed ; above and below the 
actual friction surface — that more immediately applied to the 
most prominent part of the bone — are fine reticulations of 
veins and arteries, but in the middle, in health, none are 
seen ; only the pearly-white glistening fibres shining through 
the synovial membrane. This is in somewhat striking con- 
trast with some of the other bursa, and in a physiological and 
pathological study of this particular region is not without 
much interest to the veterinary student. 
The apparent absence of vessels from these surfaces of 
contact may be owing to the greater amount of pressure or 
strain they have to sustain, directly or indirctly, while the 
animal is standing or in motion ; the particular functions of 
the tendon and, in one respect, the disadvantageous angle 
formed by the navicular bone over which it has to play, im- 
posing upon it a somewhat exceptional degree of pressure 
from the more prominent convexity of the bone ; the fibrous 
and synovial covering of the latter, of course, shares largely in 
this pressure and strain. 
But there are other features in the anatomy of this part 
which must not be overlooked, though hitherto they appear 
to have almost entirely escaped observation, notwithstanding 
their intimate relationship to the morbid changes that so 
frequently render valuable horses incurably lame and un- 
serviceable. 
As has been mentioned, the spongy nucleus of the navicular 
bone is enclosed in a comparatively thick and dense shell of 
compact tissue ; the latter is thickest at the surface correspond- 
ing to the tendon, and more particularly the lower half of that 
face — that which is most frequently involved in disease ; it is 
thinnest in the narrow face that articulates with the os pedis, 
the mean between these two being in the face which is in 
