184 ANATOMY AND PHYSIOLOGY OF THE HORSE’S FOOT. 
takes in locomotion, which is a somewhat peculiar and pro- 
minent one ; and also because of its being so very frequently 
involved in that most formidable of equine diseases — navi- 
cularthritis — the bane of horse-flesh, as it has been euphe- 
mistically designated. It is a somewhat slender flat bone, 
thicker at its lower than its upper edge, bulging considerably 
in the middle, where it shows a transverse ridge on each face, 
and becoming thinner and narrower towards the ends. Its 
position is transverse behind the joint of the foot, between 
the basilar processes, and in contact with the pedal and small 
pastern bones. Resting on, or rather articulating with, a 
portion of the posterior edge of the wide articulatory surface 
of the former bone, it very materially increases that surface 
by adding to it the width of its own upper face. This 
inclines at an angle closely approaching that of the front 
aspect of the foot-bone, and is so disposed as to fit in a 
very accurate manner into the wide posterior joint-surface of 
the coronary bone ; thus forming a capacious articular space 
affording more support for the last-named bone, and a wider 
range for its hinge-like movements. The transverse eleva- 
tion in the middle of this face, with the smooth depressions 
on each side, correspond to those on the upper surface of the 
os pedis, and these adapting themselves to the lateral con- 
vexities and central depression of the coronary bone, form, 
when covered \yith a layer of dense cartilage, and bound 
solidly together by powerful ligaments, a secure joint pos- 
sessed of extensive backward and forward motion. 
The borders of the bone offer nothing worthy of particular 
notice in this brief sketch ; they give insertion to resisting 
ligamentous bands which bind it firmly to the bones in front, 
and are pierced by many small-sized apertures for the pas- 
sage of vessels ; the two ends or wings of the bone are 
peaked upwards into somewhat rounded points that are 
buried in a thick fibrous mass which attaches them laterally 
to the pedal bone. We will notice the peculiarities of this 
fibrous structure hereafter. 
That portion of the bone which lies upon the os pedis 
(fig. 6, b) has, in early life, two distinct, though very small 
surfaces of contact, which in later years become united, 
leaving no trace of their having once been separate. 
In structure this bone is somewhat compact and strong, 
being composed of hard, closely knit, osseous tissue, enclosing 
a nucleus of looser or spongy texture which lightens and 
gives bulk to the bone, but does not by any means impair its 
desired resistance, while it affords space for the lodgment of 
blood-vessels which make the interior of this bone as vascular 
