38 



these vascular loops, by the process called cell-imbibition. 

 The cells at first are round, but gradually acquire a flattened 

 form, until, at the wearing surface they become very dense and 

 horn-like in texture. Like as in the hoof and epidermic struct- 

 tures, the outlying particles are being continually pressed upon 

 toward the external surface, and pass off in the processes of 

 wear or natural decay. In such a case absorbents are unne- 

 cessary and therefore none are present. The due secretion of 

 the synovial fluid is necessary to keep the gliding surfaces 

 of these cartilages moist, a condition necessary to the perfect 

 fulfillment of their office in the general organization. 



In chronic disease of the navicular joint, it has been ocasion- 

 ally found that these cartilages have become abraded from 

 attrition, and in some instances the cartilaginous covering of 

 the navicular bone has been found adhering to the perforans 

 tendon, of which that, bone is the fulcrum in its action upon 

 the coffin-bone. 



A KNOTTY QUESTION. 



Scarcely any question in the whole range of veterinary path- 

 ological inquiry has excited so much animated discussion and 

 such contrariety of opinion as that of the proximate cause or 

 causes of the navicular-joint disease. Few, even amongst the 

 ablest veterinary pathologists recognize more than one general 

 proximate cause for this foot affection ; and there is not a tissue 

 entering into the composition of the joint, which has not its 

 advocates for its claims to consideration as the chief tissue in- 

 volved in this complaint. Some view it as proceeding exclu- 

 sively from internal and other from external causes. The 

 bones, the cartilages, the synovia or its secreting membrane, 

 the perforans tendon, hereditary predisposition, mal-nutrition, 

 atrophy, concussion, etc., all have their separate claims put 

 forward by one writer after another for the bad pre-eminence 

 of being the chief proximate cause of this equine curse. But 

 I must not digress too far from the main course of my subject 

 or anticipate my own theory too soon. To be able satisfac- 

 torily to dispose of conflicting hypotheses, it is important that 



