538 DISEASE OF THE NAVICULAR JOINT. 



bone. In progression no inconsiderable portion of the 

 weight is cast upon the navicular bone, and by it transferred 

 to the perforans tendon ; which, however, is protected, and 

 in some measure supported, by the frog beneath. However, 

 when we consider the immense weight of the horse, in- 

 creased by motion as well as by the burden of a rider, it 

 cannot be wondered at if the protection and support some- 

 times prove weaker than is required. The tendon receives, 

 in all cases, the first injury. Often the occasion is marked 

 by instantaneous lameness ; at other times it is slow in 

 coming on, and often repeated before the disease is con- 

 firmed. Between the bone and the tendon is situated a 

 synovial capsule, which facilitates the independent motions 

 of each upon the other. The first consequence of injury is 

 inflammation. Inflammation of the tendon is readily com- 

 municated to the synovial capsule ; the secretion of the 

 lubricating fluid is thereupon stopped ; friction takes place 

 as a consequence ; the navicular bone is denuded of its arti- 

 cular cartilage ; ulceration is ultimately established ; this may 

 end in the absorption of the synovial sac, and the junction 

 of the bone to the tendon ; it may terminate in the fracture 

 of the bone, and it may also conclude with the rupture of 

 the tendon. In case of the first termination the horse is 

 groggy ever after, and when either of the two last termina- 

 tions occur it is better to order the animal to be imme- 

 diately destroyed, for his service in this world is at an end. 

 The symptoms are various, according to the progress made 

 by the disease. At first the horse is lame, and the cause 

 can be discovered in no other part than the foot. If the 

 animal be now narrowly observed, when at rest, and within 

 the stable, he will be seen to favour one foot, and to have 

 the diseased one slightly in advance of the other ; should 

 the animal now be taken out and ridden he goes forth lame 

 and returns home sound, for the warmth of exertion forces 

 back the absent synovia. Should the disease progress to 

 the ulcerative stage, the lameness has, like toothache, 

 moments of uncertain ease, but more or less it keeps on. 

 The foot is now generally advanced or pointed ; the frog 

 narrows, hardens, becomes elevated, and is continually 

 emitting a loathsome thrush ; the sole likewise grows 

 more thick and more high, the quarters become considera- 



