REVIEWS. 45 7 
outer, but both crusts are originally secreted in a fluid state, and subse- 
quently become of the requisite consistency. 
“ If we take an extended view of the matter, and call in the aid of compa- 
rative anatomy, we shall be led to consider the uses of the frog as of a mixed 
nature. Eminently simple in form and structure, it combines even more 
than the qualities possessed by the tendo-cartilaginous balls at the posterior 
part of the feet of the digitated tribes, as dogs, cats, &c. It is more dense 
in structure, to resist the weight imposed on it ; yet more truly elastic, to 
enable it to preserve its own integrity under the increased pressure of 
so large an animal, and to transfer the shock of motion more uniformly 
over the limb. It is peculiar also in being united at its apex ; but it is 
wisely disunited by its cleft at its posterior portion, where it can best act on 
the yielding walls of the hoof. This union, or separation indeed, arises from 
the frog being formed of a continuation of the coronet. The frog claims, 
likewise, importance as a natural wedge, to prevent slipping and sliding on 
smooth surfaces. It is reasonable also to suppose, that it forms a valuable 
antagonist to the downward and backward direction of the internal parts of 
the foot ; and in this way it may offer a point of solid support to the flexor 
tendon, and an important protection to the navicular bone ; it also most 
unquestionably acts very favorably in; promoting the expansion of the 
hoof. 
“The bars . — We have already fully explained that the crust of the hoof 
does not terminate at the heels, as a superficial observation might lead one 
to conclude ; but that having gained the heels, it turns inwards and forwards, 
decreasing in extent, and laying itself on each side of the frog.” 
THE INTERIOR OF THE FOOT. 
“The part that presents itself when the hoof is removed, is the sensitive or 
fleshy sole , which is a vascular expansion covering a considerable portion of 
the under surface of the coffin bone, and extending beyond its posterior 
part, but leaving a triangular space for the vascular expansion of the sensi- 
tive frog. As the sensitive sole passes behind the coffin bone it becomes 
thicker, and attaches itself to the inferior cartilages. The sensitive sole 
upon its upper surface is of a ligamentous nature, but the underneath is 
vascular ; and from it is secreted the horny sole. The vascularity of this 
part renders it very susceptible of inflammation. The sensitive frog presents 
a very curious structure of ligamentous and tendinous expansions above ; 
but covered underneath by a horny coating, corresponding in shape to the 
sensitive frog, and secreted from it. It lies in an interval within the sen- 
sitive sole, attached by its point to the inferior surface of the coffin bone, 
with its heels expanding posteriorly ; being a continuation of the secretive 
coronet, and attached to the cartilaginous substance, united with cellular 
and fluid matter. The lateral critilages , one to each side, are fixed into a 
groove, upon the upper surface of each wing of the coffin bone. Independent 
of their bony attachment, they are also retained in their situation by means 
of ligamentous fibres, and by lateral connexions. They are externally convex, 
internally they are concave ; highest in the centre, but thinner and smaller 
towards the extremities : their inferior portions pass under the wings of the 
coffin bone, and unite with the semi-cartilaginous substance of the elastic 
frog. The lateral cartilages are partly within and partly without the hoof ; 
are covered at their lower portion by the coronary ligament, which, by being 
extended over them, prevents their too great dilatation. To the lower part of 
their external surface the laminae gain an attachment ; and within their in- 
ternal portion is lodged the substance forming the upper and posterior part 
of the elastic frog. The uses of these cartilages, as before observed, are con- 
xxvii. 60 
