164 LAMENESS OP THE HORSE 



is the difficulty with which the subject supports weight with 

 one foot. It is this which causes the victim to stand as if 

 "rooted to the ground" when all four feet are involved. If one 

 attempts to take up one foot, thus causing the subject to stand 

 on the other, there is much resistance and in many eases the 

 animal refuses to give the foot. 



When we consider that the sensitive parts of the foot are 

 encased by a horny, unyielding box and that, when the laminae 

 are congested, a great pressure is brought to bear upon the sensi- 

 tive structures, it is easy to understand why the condition is so 

 painful. 



Chronic laminitis is a sequel of acute inflammation of the sensi- 

 tive laminae. It varies as to intensity and the exact manner 

 of its manifestation depends upon preexisting disturbances. 



In some mild cases of laminitis there are recurrent attacks 

 wherein no particular structural change exists, and diagnosis 

 is established chiefly by noting the character of the pulse at the 

 bifurcation of the large metacarpal (or metatarsal) artery just 

 above the fetlock. The same manifestation of pain is present 

 when weight is supported by one foot, though in a lesser degree. 

 There is less local heat to be detected by palpation than in 

 the acute cases. 



Chronic laminitis as it occurs following acute attacks which 

 have resulted in structural changes of the foot, present the same 

 symptoms just described and, in addition, the j^eculiar altera- 

 tions in structure exist. When, owing to acute inflammation of 

 the sensitive laminae, there has resulted necrosis of this sensitive 

 tissue together with infiltration between the anterior surface of 

 the distal phalanx (os pedis) and the contacting hoof, the lower 

 portion of the distal phalanx is turned downward and backward 

 (rotated upon its transverse axis). Because of the traction 

 which is exerted by the deep flexor tendon (perforans), as it 

 attaches to the solar surface of the distal phalanx, this rotation 

 is facilitated. With hyperplasia of lamina, at the anterior por- 

 tion of the distal phalanx, there results a thick "white line." 

 Rotation of the distal phalanx necessitates a descent of its apical 

 portion and there occurs a "dropped sole." 



