REVIEW. 
153 
a 4. That dilatation, resulting from such accumulated pres- 
sion, becomes manifest— a, All round the upper margin of the 
hoof, where the thin crust generally yields to the stress upon 
the coronet:— b, To a more sensible degree in the bulbs of the 
cartilages and plantar cushion (fatty frog), which exert a di¬ 
lating force upon the heels of the frog, and upon the arched 
replications of the periople, producing descent ( renversement ) 
of them backwards:— c, And, lastly, upon the inferior circum¬ 
ference of the wall, at the posterior parts of the quarters, on a 
level with the heels, where expansion becomes the result of the 
combined action of the sole, bars, and frog, the tendency of such 
being to produce an expansive ( eccentrique ) action under the 
impression of force from above. 
“ This eccentric or expansive motion becomes the more 
perceptible the greater the pression exerted upon the pos¬ 
terior parts of the hoof. For example, it is greatest when a 
horse is at his fullest speed, as the moment that the pasterns, 
in consequence of the fetlock joint being tensely extended, are 
depressed to that degree, that they approach a horizontal line, 
occasioning intumescence of the bulbs of the fatty-frog in the 
interval between the cartilages, and pressing at the same moment 
with all their weight upon the cone of the frog, (the frog-stay) ; 
constituting a mechanical contrivance of that felicitous nature 
that the spring of the hoof regulates itself by the force of the 
effort it has to sustain. 
“ Bracy Clark has much exaggerated all this expansive 
action, and hence the fruitless expenditure of money and 
thought the construction of his jointed shoe has put him to. 
While the different patented shoes of Coleman, which have 
turned out but an invention malheureuse , evince the same 
over-rating. 
“ So that—and on this point M. Bouley insists, it being with 
him a principle—what is called its dilatability, expansibility, or 
elasticity, amounts to the hoof not being regarded as a fixed 
body; at the same time, its rigidity is not such as to refuse ex¬ 
pansion to the internal parts of the foot, though within limits so 
restricted, that the spring excited in it is scarcely perceptible to 
our means of detection. 
“ It is not, therefore, in the hoof itself, viewed as a mechanical 
body, that the greatest elastic power resides, but in the parts 
enclosed within the hoof. These parts it is which, by virtue 
of the properties they enjoy of dilatation, contraction, and ex¬ 
pansion, change their form under the influence of pression, and 
thus are enabled to deaden and annihilate, through their supple¬ 
ness of substance, all ultimate effect of shock, &c. 
“ The compressibility they are capable of, which admits of their 
