DISEASES. 617 



not noticed from the outside, or showing but a sHght depression 

 on the surface of the waU. These cracks are only discoverable 

 when the foot has been weU pared down. As shght as the solu- 

 tion of continuity may be, it participates in the motion of dilata- 

 tion of the foot, and it is better detected when the foot is raised 

 than when it rests on the ground. This is the case when it is a toe- 

 crack, but on the contrary, the quarter-crack is more open when 

 the animal rests its weight on the leg, in which case, the sepa- 

 ration of the borders of the cracks may be from two to four mUli- 

 metres, and may expose the bottom of the fissure. Ordinarily, 

 cracks appear first at the coronet, and there is then but a sHght 

 opening, but as they become older, and grow down, they have a 

 tendency to become deeper and more complete. When of old 

 standing, their borders are rough and scaly, having between them 

 an ulcerated tissue and sometimes a fungus growth, from which 

 escapes a sanious fluid. In other cases, as of quarter-crack, the 

 edges have a tendency to cover each other. 



Superficial cracks are not always attended with lameness ; it is, 

 on the contrary, often very severe when they are deep. The pain 

 is generally in proportion to the depth and degree of opening of 

 the fissure, and also especially to any comphcations which may 

 exist in the tissues beneath. The lameness seems at times to be 

 due to the injury of the deep, soft tissues, and to be caused by the 

 motions of the horny box when they become pinched, irritated 

 and bruised. The affected animals are especially lame when the 

 foot rests on the ground, and the lameness is greater on a hard 

 than on a soft surface. If an animal suffering with toe-cracks is 

 moved on descending ground, the lameness is greater than on 

 ascending a lull, the weight of the toe in the latter case producing 

 less opening of the edges of the solution of continuity. In quarter- 

 cracks, the severity of the lameness is always in proportion to the 

 rapidity of the gait; many horses which are but slightly lame on 

 a jog, become much more so when the gait is accelerated, the dila- 

 tion of the heels being greater, and the separation of the b rders 

 of the crack increasing in proportion to the speed. When there 

 is lameness, there is naturally an increase of heat and sensibUity 

 of the foot, especially at the seat of the crack. This is often dis- 

 covered by feeling with the hand ; old cracks are generally accom- 

 panied by a thickening existing at a corresponding point of the 

 hoof. A deep, but recent crack, is apt to be accompanied with 



