STRUCTURE OF THE HORSE. 99 



dred. The superior or corinar\' border of the wall shows a gutter, 

 t-enned the cutigeral groove, which is the mould left by the coro- 

 nary cushion. The inferior border embraces the sole, and in the 

 unshod animal comes into contact with the ground. 



The sole is a thick plate of horn, which helps to form the 

 inferior portion of the hoof. It is comprised between the inner 

 border of the inferior part of the wall and the inflection of the 

 bars. The inferior or external surface forms a vault, which is 

 more or less concave in different animals. The superior face is 

 somewhat convex, and has a punctuated appearance, similar to 

 that already seen in the cutigeral groove. The minute holes 

 lodge the papillae of the so-called sensitive sole, which is the 

 horn-secreting structure of this region. Anteriorly the sole 

 presents a convex border, which unites it intimately to the lower 

 border of the wall, a line of whitish horn marking the junction 

 of the two structures. Posteriorly, it has a deep Y-shaped in- 

 dentation, into the central point of which the frog penetrates. 



The frog is an elastic mass of horn, which in a state of nature 

 projects sufficiently to come in contact with the ground, and thus 

 give the animal a secure foothold. Its inferior surface shows 

 posteriorly a shallow cleft, or depression, termed the median 

 lacuna. The superior surface shows a projection termed the 

 frog-stay. On each side of the frog-stay this surface is depressed, 

 and the whole is moulded on the plantar cushion. The base or 

 posterior extremities constitute the heels or bulbs of the frog; 

 these are two round, flexible, and elastic eminences formed by 

 two extremities, and separated by the cleft. The anterior ex- 

 tremity, or point, is wedged into the center of the sok'. The 

 lateral borders bring the frog into relation with the bars and the 

 sole, and there is an intimate union with each of these at the 

 point of contact. The parts contained within the hoof are the 

 OS pedis, 05 navicular, the distal extremity of the os coronse, the 

 ligaments by which these are connected together, the insertion 

 of the extensor pedis and flexor perforans tendon and the vessels 

 and nerves. There are also certain stmctures proper to the 



