ANATOMY OF THE HORSE. 
3G7 
euticular surface—those issuing out of the interior of the bone 
simply passing through (without ramifying within) the fibrous 
substance : so that, if the substance of the sole be laid open by 
transverse section, the incised edge, near the surface, exhibits a 
deep red tint, while the interior, nearer the bone, has a pinkish 
or pale red aspect. 
The Sensitive Frog. 
Under this head is included the cleft cuneiform body, pro¬ 
jecting from the bottom of the foot, together with the substance 
continued from it and filling the interval between the cartilages. 
Sainbel calls it “ the fleshy frog.” 
Division.— We distinguish, in the sensitive as in the horny 
frog, an apex or toe; two heels, separated by the cleft; and a 
portion intermediate between these, which is the hocly. 
Situation and Connexion. —The sensitive frog occupies the 
posterior and central parts of the bottom of the foot, forming in 
the tread a firm and secure point d’appui. Being in the hoofless 
foot equally prominent with the projecting edge of the coffin- 
bone, one might be led to infer that the horny frog should take 
the same line of bearing with the crust. The frog, altogether, 
is lodged in a capacious irregular space, bounded superiorly by 
the tendo-perforans and common skin, laterally by the cartilages, 
and interiorly by the horny frog: with all which parts it has con¬ 
nexions ; besides being continuous with the sensitive bars and 
sole, and at the heels with the coronary substance. On its sides 
are two shallow ill-defined hollows, corresponding to the com¬ 
missures of the horny frog, into which are received the horny 
prominences opposed to them. 
Structure.— Entering into the composition of this body we 
distinguish four parts:—An exterior or euticular covering; a 
congeries , or network of bloodvessels; a fibro-cartilaginous texture; 
and an elastic interstitial matter. 
The exterior or euticular covering invests the prominent bul¬ 
bous portion of the frog, and also gives a lining to the cleft. 
Superiorly, it is continuous with the skin descending upon the 
heels; anteriorly, with the euticular covering of the coronet; in¬ 
teriorly, with thatof the sole. Numerous villous processes sprout 
from its surface, and enter the porosities in the interior of the 
horny frog, taking a direction downward and forward, the same 
as that in which the fibres of the horn grow. 
The vascular covering succeeds the euticular, lying immediately 
underneath it. It consists of a network of bloodvessels, princi¬ 
pally veins, but which are not so thickly set as upon the sole. 
The fibro-cartilaginous case comes next. We find it spread 
