EXPANSION AT CORONARY BORDER. 125 



distance. In the region of the heels, on the other hand, there 

 is distinct dilatation ; the coronary border of the heels bulges 

 outwards, a condition clearly visible in hoofs in which the 

 coronary border is well curved. Where, however, the latter is 

 straight, bulging is imperceptible or fails to occur. The bulbs 

 of the heels swell, and are thrust somewhat backwards and 

 downwards. If, now, the fetlock rises, the dilatation of the 

 coronary border of the heels disappears in a forward direction 

 like a fluid wave and with a rapidity proportioned to the speed 

 of ascent of the fetlock ; while the contraction of the lateral 

 and anterior regions of the coronary border is replaced, 

 immediately the foot is lifted, by slight swelling and dilata- 

 tion of the coronary border of the toe. With the renewed 

 sinking of the fetlock these changes of form are repeated in 

 inverse order. Low, Hat, broad hoofs show^ these changes more 

 distinctly than those which are deep and upright. Absolute 

 rest of the coronary border (at least while the animal is stand- 

 ing on the foot) is inconceivable, for the slightest movement of 

 the body immediately evokes some change in its form. The 

 coronary border of the hoof may be compared with an exceed- 

 ingly elastic ring which yields to the slightest pressure of the 

 body-weight, dilatation at one part producing a corresponding 

 retraction at another. The great elasticity of this ring is due 

 to the perioplic horn, which is found at the points where the 

 greatest movement occurs — along the quarters as far as the 

 bulbs, and at the toe front. Permanent defects in the position 

 of the limbs (such as knuckling, etc.) interfere witli the normal 

 function of the coronary border, and may be followed by 

 irregular formation and distortion of the hoof. 



2. Movement at the bearing margin or ground surface 

 differs somewhat from that at the coronary border. In front, 

 and as far as the centre of the quarter, no distinct change 

 occurs ; from the centre of the quarter, how^ever, to the end of 

 the bearing surface (fig. 71) it is always possible to demon- 

 strate dilatation in sound, unshod hoofs, especially when the 

 horny sole and horny frog are supported. The amount, of 

 this dilatation varies, with the weight on the foot, from 0*1 to 

 1*5 millimetre at either side, while it is also greatly depend- 

 ant on the angle formed by the heel with the ground. In 

 heels which converge in their course from above downwards 



