THE FOOT. 293 



whilst the crust exhibits perpendicular striae, corresponding 

 with the laminae; but this is not well shown in Fig. 13. In 

 examining the cut of the sole, Fig. 15, it will be seen that the 

 crust is bent inwards towards the frog at the heel on each side ; 

 there are the bars, which in the natural foot appear as sharpened 

 prominences, extending from the heels into the centre of the foot, 

 between the sole and the frog, and which are useful as buttresses, 

 supporting the crust from being crushed inwards by the superin- 

 cumbent weight. The sole is the plate at the bottom of the foot, 

 which should be slightly concave downwards, and is fixed to the 

 inner edge of the crust, and the outer sides of the bars, and not to 

 their lower surfaces. Its usual thickness is about one-sixth of an 

 inch, but it will vary greatly in different horses, and it is thicker 

 where it runs back between the bars and the crust. It is secreted 

 in plates, which can readily be separated with a knife in that 

 direction. The frog is the prominent, triangular, and elastic 

 substance, which fills up the space between the heels posteriorly, 

 the bars on each side, and the sole in front. In the middle is a 

 longitudinal fissflre, called the cleft, the sides of which should 

 form an angle of about forty-five degrees. In front of this cleft 

 is a solid wedge of the elastic horny substance, constituting the 

 frog, which lies immediately beneath the navicular bone and 

 has received the name of the cushion. Posteriorly it is spread 

 out into a thin band on each side which covers the bulbs of 

 the heels, and passes round the upper part of the wall constituting 

 the coronary frog-band of Bracy Clark, which is continuous with 

 the coronary substance. The structure of the horn which forms 

 these three divisions, varies a good deal. In the crust it is fibrous, 

 somewhat resembling whalebone in this respect, but not ^uite so 

 hard ] these bristly fibres are united by a gelatinous substance, but 

 they are arranged so as to lie in straight lines descending from the 

 coronary circle to the ground. The wall may, therefore, be 

 considered as composed of hairs agglutinated together, and each 

 secreted by one of the villi, which are so thickly spread over the 

 surface of the coronary circle. The sole is also fibrous, but not 

 nearly so much so as the wall \ and the fibres are not arranged in 

 so parallel a manner, taking rather an oblique direction from 

 behind forwards, and being more easily separated into scales. 

 The frog differs from both, in possessing finer fibres and in smaller 

 quantity, in comparison with the gelatine, which formation renders 

 it more soft and elastic and also more prone to decomposition. 

 The horny matter is sometimes colored a grayish brown, some- 

 times white, and sometimes marbled by a mixture of the two 

 colors. 



THE HOOF is developed by secretion, which has its seat in the 

 coronary substance and laminae. It consists in a pouring out on 

 25* 



