880 RING-BONE. 



Iii articular ring-bone the exostosis extends from either side over 

 the anterior surface of the joint, and appears more or less circular, 

 from which circumstance it has received its name. The posterior 

 surface is covered l>\ the ligaments and flexor tendons, and therefore 

 cannot well be examined. The exostosis sometimes arises chiefly 

 from the suffraginis, and Ls then rather high placed, sometimes from 

 the os c-iroii.c. or os pedis, when it is found either just above or within 

 the hoof. High and low forms of ring-bone have therefore been 

 distinguished. The swelling is hard, painless on pressure, and the 

 skin covering it is movable. 



The periarticular form Ls similar in appearance, except that the 

 enlargement is usually confined to the lateral surfaces of the 

 suffraginis and coronet bones, and the anterior surface is usually 

 normal. As in the former case, the swelling may appear higher 

 or lower, and in general what has been said above also applies to 

 this form. 



Lameness is a constant feature of articular ring-bone, and often 

 accompanies the periarticular form. It occurs principally when 

 weight is placed on the limb, and is sometimes considerable, some- 

 times only slight. Lameness may be absent in rachitic ring-bone ; 

 and usually in simple exostosis on the pastern there is no sign of 

 lameness. After a long rest it may partly disappear, and in spirited 

 animals slight lameness is often lost during movement. When the 

 condition has become chronic, the muscles of the limb atrophy, 

 wasting being proportioned to the chronicity and severity of the 

 lameness. As a rule the later phase of the stride is considerably 

 shortened, and the phalanges show volar flexion, i.e., the fetlock 

 is upright. In the periarticular form, lameness is best seen when 

 the animal turns in short circles towards the diseased side. It is a 

 consequence of inflammation of the articular surfaces or of ligaments, 

 though at times it results from mechanical obstruction to movement 

 in the coronary joint, due either to the formation of exostoses or to 

 thickening of ligaments, and adhesions around the articular surfaces. 

 Such adhesions are often accompanied by excessive volar flexion. 

 By lifting the foot the anchylosis of the joint is discovered immediately 

 an attempt is made to rotate, to flex, or to extend it. From the 

 above it will be clear that the degree of lameness in no way 

 depends on the size of the exostosis ; a large exostosis may only 

 produce slight lameness, and vice versa. 



The diagnosis of ring-bone is very difficult unless the enlargement 

 is well developed. In foals the phalangeal epiphyses appear well 

 developed, and the coronet -joint lies high in consequence of incomplete 



