590 THE SENSE ORGANS AND SKIN OF THE HORSE 
fece of the hoof. It is somewhat erescentie in outline, and presents two surfaces 
and two borders. The internal surface is convex, and slopes with a varying 
degree of obliquity downward to the convex border. It presents numerous small 
funnel-like openings which contain the papillae of the sole coritum in the natural 
state. The external or ground surface is the converse of the preceding. It is nor- 
mally arched—and more strongly in the hind than in the fore foot—but the curvature 
is subject to wide variation; in heavy draft horses the sole is commonly less curved 
than in the lighter breeds and may even be flat. The surface is usually rough, since 
the horn exfoliates here in irregular flakes. The convex border is joined to the wall by 
relatively soft horn, previously referred to as forming the white line on the ground 
surface of the hoof. The angle of junction is rounded internally and presents a 
Fic. 713.—Riaut Forr Hoor or Horse; Grounp SurFrace. 
4, bar; 5, sole; 5’, angle of sole; 6, white 
apex of frog; 8, central sulcus of frog; 9, 9, collateral sulci between frog and bars; 
1, Basal or ground border of wall; 2, lamine of wall; 3, angle of wall 
line (junction of wail and sole); 7, 
10, 10, bulbs of hoef. 
number of low ridges and specially large openings for the papillsee of the corium. 
There is frequently a ridge of larger size at the toe. The concave border has the 
form of a deep angle which is occupied by the bars and frog. It concurs in part 
with these in forming two pronounced ridges in the interior of the foot. The parts 
of the sole between the wall and bars are termed its angles (Anguli sole). 
3. The frog (Cuneus ungulz) is a wedge-shaped mass which occupies the angle 
bounded by the bars and sole, and extends considerably below these on the ground 
suriace of the foot. It may be deseribed as having four surfaces, a base, and an 
apex. The internal surface bears a central ridge, the spine or “‘frog-stay”’ (Spina 
cunei ungulse), which is high posteriorly and subsides abruptly in front. On either 
side of this there is a deep depression, which is bounded outwardly by the rounded 
