86 



THE PROTECTIVE STRUCTURES OF THE FOOT. 



sensitive wall mentioned on page 72. It is difficult to ascribe 

 any particular purpose to this prominence, which is not in- 

 variably present. The degree of convexity of the upper sur- 

 face of the sole varies greatly in different hoofs, being, cmteris 

 paribus, greater in hind than in fore feet, while in diseased 

 hoofs it may be entirely suppressed or the hoof may even be 

 concave. 



The upper surface of the sole, like the cutigeral groove, is 

 dotted with small holes, the openings of little funnel-shaped 



canals of varying size, which 



horn -secreting 

 the sensitive 



Fig. 53. — Vertical section from sole, magnified. 

 «, funnel-shaped openings in which are lodged 

 the horn-secreting papillfe of the sole ; they 

 vary in size; 6, horny tubules ; c, intermediary 

 horn . 



lodge the 

 papilla' of 

 sole. 



The under surface usually 

 presents a concavity corre- 

 sponding to the convexity of 

 the upper, though in horses 

 kept in the stable this space 

 may be filled by masses of 

 horn which would otherwise 

 have been shed. In a nor- 

 mal foot the most marked 

 concavity is near the point of the frog, whence the sole falls 

 towards the wall. 



The outer border of the sole is usually somewhat weaker 

 than the centre. It corresponds in shape to the form of the 

 wall, that is, in fore-feet it is nearly circular, in hind-feet more 

 or less oval, and is attached to the lower portion of the wall 

 through the medium of the white line. The inner triangular 

 space for the reception of the frog is bordered, not by the sole, 

 but by the bars, which throughout its greater extent can be 

 differentiated from the sole by following the wliite line. The 

 anterior part of this border is formed by a fusion between the 

 horn of the bars and sole ; to it is attached the point of the 

 horny frog. 



The white line (figs. 45, 46,^, and 48, h) consists of portions of 

 the laminal sheath of the wall, which by continued growth are 

 carried down and appear between the horny sole and the 

 bearing surface of the wall. On careful examination, the 

 individual laminae may be distinguished at the white line as 



