NAVICULARTHRITIS. 169 



in its substance, which hereabouts is rather of the nature of carti- 

 lage than tendon. And both these cartilaginous surfaces being 

 lined by a delicate vascular (.9t/7iomaZ) membrane, the same as other 

 bursal cavities are, which continually exudes joint-oil, the play of 

 one upon the other is at once rendered facile and frictionless. 



Now, it is either the said crest across the navicular bone or 

 the opposed concavity in the tendon, or both together, which shew 

 the earliest signs of disease in cases of navicularthritis : of the 

 two, Mr. Turner seems to give the priority to the tendon ; whereas 

 Dr. Brauell informs us, his observations have proved to him 

 that neither the navicular bone nor the bursa is the invariable 

 nidus of incipient disease, " it being as likely to arise in one tissue 

 as the other;" and adds, " that when the bone is primitively 

 attacked, the disease develops itself tardily and insensibly ; but 

 that in the tendon the evolution of navicularthritis is comparatively 

 rapid and decided." Let which part will be first attacked, it is 

 pretty evident that the opposed surface soon takes on the morbid 

 action, either from direct contact, or, as Brauell says, from " sym- 

 pathy :" the curious accompanying fact being — one that casts a 

 strong light upon the etiology of navicularthritis — that the upper 

 or cofBn-ioint surface of the navicular bone, although covered with 

 articular cartilage the same as the lower, has not, on any occasion 

 whatever, been found a participator in the disease. " I have fre- 

 quently seen," says Mr. Turner, " in long-standing cases of navi- 

 cular disease, not only all the cartilage of the inferior surface of 

 the bone ulcerated, but also a material part of this small bone 

 absorbed — almost annihilated — and yet found its upper surface 

 sound, with the cartilage entire, and the synovial membrane quite 

 perfect." 



The morbid appearances presented by the navicular bursa 

 of a horse who during life had been the subject of lameness from 

 navicular disease, will vary according to the stage the disease 

 happens to be in at the time of death, and will also be influenced 

 by the treatment the animal may have undergone for it during 

 life. It is only by chance that, in the early stages of navicular- 

 thritis, opportunities offer for post-mortem inspections; though 

 in the latter or groggy stages opportunities abound: it being 



VOL. IV. Z 



