EXTERNAL PARTS OF THE FOOT 225 



gether by a fibrous texture, many of which have 

 the property of secreting the horny substance which 

 forms the crust. The sensible laminae, a, fig. 9, 

 have the power of secreting some horn, which 

 furnishes an immediate defence against injury in 

 cases where the crust is either purposely removed, 

 or has sustained injury. This is sufficient proof in 

 cases of quittor or sand-crack, when it becomes 

 absolutely necessary to remove a portion of the 

 crust. The exposed portion is soon covered by a 

 film of a hard horny texture. The crust, however, 

 is chiefly formed by the coronary ligament ; and 

 hence in quittor and sand-crack its growth is slow 

 and downwards, and is only replaced with the 

 natural lengthening of the crust, in the same manner 

 as in injury to the human nail. And there is situate 

 below the coronary ligament a strip of horny matter, 

 emanating from the frog, which seem.s intended for 

 a similar purpose to that which surrounds the root 

 of the human nail — namely, to strengthen the union 

 of the part where it rests, and to bind together the 

 various substances which meet there. 



The crust is composed of numerous fibres, which 

 proceed directly from the coronet to the ground, 

 but which follow an oblique course from the heel 

 forwards. These fibres are kept together by a 

 glutinous substance. 



In a sound condition the crust of the foot is 

 smooth and hard, and when there are rings or other 

 thickenings, it is a sure indication of disease in the 

 foot, and that, too, to a considerable extent, as may 

 be well supposed, to induce this irregularity of 

 growth. When the front is depressed, it may be 

 inferred that a sinking of the coffin bone has taken 

 place, and that the sole will be flat and pumiced. 



p 



