178 ANATOMY AND PHYSIOLOGY OP THE HORSE , S FOOT. 
with another, that the substance of this portion looks quite 
spongy. This expansion of the bony tissue is carried to its 
greatest extent towards the wings, where the bone becomes 
light and porous like a piece of pumice-stone, and there forms 
two irregularly-shaped scaly surfaces, or nodes, full of small 
cavities, and which have been termed the patilobe eminences 
(fig. 4, k), though they are usually but little elevated above 
the adjoining level. The whole surface is channelled and 
pierced in a somewhat irregular manner for the transmission 
of blood-vessels ; while its roughness admirably disposes it 
for the attachment of important textures, which will be 
described hereafter. 
If we now look at the sole or plantar surface of the bone, 
we will find something analogous in structure. Sufficiently 
concave to form a good arch, on which the horny sole is 
moulded, its thickest, densest, and most unyielding part is 
in the centre — the keystone of the arch, and the most concave 
portion, which has to withstand the severest tests imposed, 
perhaps, upon any part of the limb. From this sustaining 
disposition of the bone-tissue at this spot, and which occupies 
more than one half of the plantar face, the laminated texture 
begins gradually to open out in diverging lines, throwing 
communicating fibres across to each other as they radiate 
from the centre, until, on reaching the circumference, they 
are found to bear the same relation with regard to porosity 
and lightness which the front fibres do. Here they all meet 
in a thin border, the anterior convex or lower edge (fig. 4, d), 
which is generally dentated or slightly notched, though 
sometimes it is tolerably even; in this way, and by reason of 
their direction and mode of communication, they strengthen 
each other. Besides supporting the weight, the surface at 
its densest part has to sustain the insertion and traction of 
the large flexor tendon of the limb, one of the strongest in 
the body, as well as afford a bed for the horny sole. It 
may be observed, however, that the sole of the bone alto- 
gether is much more extensively enveloped in a close covering 
of osseous tissue than the anterior surface. 
Thus is a given quantity of bone material put to the 
greatest use in securing strength where most needed ; being 
sparingly, yet most judiciously expanded into a wide ample 
surface, it gives the necessary superficies with diminution of 
weight ; and, in addition, being disposed in a particular 
manner, and pierced by judiciously arranged communicating 
cells, it enables the whole to resist the downward pressure 
without danger to the nutrient vessels sheltered in its interior. 
Such a disposition also tends to diminish that tendency to 
