NAVICULAR DISEASE. 347 



face of all articular cartilages. — (See Fig. 3G.) It is true that 

 the navicular bone, like the sesamoids and the bicipital groove 

 of the humerus, is covered by a cartilage with fibrous tissue im- 

 bedded in its matrix, but there is no membrane on the surface. 



The phenomena observable during the course of the disease" 

 here call for remark, more especially the variation in the point- 

 ing of the feet. One animal will exhibit this sign before any 

 lameness is manifested, whilst another will have been lame for 

 some time before it begins to point. In the first instance, the 

 pain in the part is due to a very slight degree of inflammatory 

 action, and marks a slow, insidious development of the disease ; 

 there is sufficient pain to cause uneasiness whilst the animal is at 

 rest, and when his attention is not called away from it ; but when 

 at work, the excitement of exercise, more especially if he be a 

 high-spirited horse, makes him forget his pain, or the pain itself 

 is dissipated by movement. In the other case, sufficient injury 

 has been inflicted to cause immediate lameness, and this may 

 last for some time before the animal becomes habituated 

 to the method by which some degree of relief is secured by 

 pointing. The act of pointing is performed in two ways : — 1st. 

 By extension of the limb and of the pastern, the heel of the foot 

 resting upon the ground, the leg stretched forward before ita 

 fellow. In this form relief is obtained by the increased obliquity 

 oC the pastern, and by an endeavour to approximate the column 

 of bones to their natural* position, whereby weight is taken off 

 the navicular bone. The other method is by flexing the limb, 

 touching the ground with the toe only, the heel elevated, 

 the flexor aspect of the limb relaxed, and the inflamed part 

 relieved of tension and pressure as much as possible. This 

 foiTO is indicative of more advanced disease than the former, of 

 denudation of the osseous cancelli, and fibrillisation of the tendon. 



The concavity of the sole of the foot is grailually increased, 

 and the frog hardened and elevated from the ground, or soft- 

 ened by a discharge from its cleft and surface. These changes 

 are, however, but a part of the general atrophy of the foot ; there 

 is decreased functional activity ; tlie heel is not brought firmly 

 to the ground, and ita structure wastes or becomes diseased. 



In discussing the causes of the disease, I have stated my 

 opinion that generally the alteration in the direction of the 

 bony column by the shoe, or by a natural upright conformation 



