EXTERNAL PARTS OF THE FOOT. 253 



the quarters and heels. This will show the necessity for 

 shoeing-smiths being adepts in driving the nails, seeing the 

 small space for that purpose, and more especially behind. 

 The crust is thinner and a little higher in the inner than 

 the outer quarter. This is another beautiful provision, 

 because, being placed under the inner splint-bone, more of 

 the weight rests on the inside than the outside, consequently 

 it is enabled to expand more, and thus by its elasticity assists 

 in lessening concussion. When, therefore, expansion is pre- 

 vented by the inner quarter being nailed firmly to the shoe, 

 corns, contraction, and sand-crack are induced. The crust 

 is not liable to much variation in thickness, as will be seen 

 by a reference to plate vi. fig. 10, z^ and v, and c in fig. 9, 

 until near the top, at the coronet, or where the horn of the 

 hoof unites with the skin of the pasterns, where it becomes 

 abruptly thin, as will be seen on a reference to 5, in fig. 10. 

 Here it appears as if scooped out, and here also its colour 

 and consistence are changed, and it appears like a continua- 

 tion of the skin. This thin portion is called the coronary 

 ring, r, fig. 10, which covers a thickened prolongation of 

 the skin called the coronary ligament, (?, in fig. 9. This 

 extension of the skin is supplied with numerous densely set 

 blood-vessels, connected together by a fibrous texture, many 

 of which have the property of secreting the horny sub- 

 stance which forms the crust. The sensible laminae, a, ^g, 

 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 in- 

 jury. 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 



