430 DISEASES OF THE HORSE'S FOOT 



then progressed until destruction of the secreting layer of 

 the bursal membrane has been seriously interfered with, 

 and in this case we find a distinct deficiency in the quantity 

 of synovia in the bursa. In advanced cases it is even 

 found that the bursa is absolutely dry. 



2. Changes in the Cartilage. — Directly that portion of the 

 bursal membrane covering the cartilage is the subject of 

 inflammatory change, the cartilage itself, by reason of its 

 low vitality, soon suffers. 



Under a process, which we may term ' dry ulcerative,' 

 the cartilage covering the ridge on the lower surface of the 

 bone commences to become eroded, and in appearance has 

 been likened, both by English and Continental writers, to a 

 piece of wood that has been worm-eaten (see Fig. 161). 



Fig. 161. — Navicular Bone (Postero-inferior Surface) showing 

 the 'Worm-eaten' appearance caused by Erosion of the 

 Hyaline Cartilage, and commencing Rarefactive Arthritis. 



' At this stage, or much earlier ' — we are quoting Colonel 

 Smith, A.V.D.— * may be found calcareous deposits in the 

 fibro-cartilage and the bone. They are scattered like fine 

 sand here and there, generally across the inferior half of 

 the face of the bone; they. are sometimes numerous, fre- 

 quently scanty, occasionally entirely absent. The amount 

 of calcareous degeneration depends upon the lesions pres- 

 ent. If much destruction of bone exists, there will be but 

 few calcareous deposits ; whilst if there are many calcareous 

 deposits, there may be but slight ulceration of bone tissue, 

 and perhaps none at all. In fact, I have held the opinion, 

 and see no reason to modify it, that calcareous deposits are 

 safeguards against caries.'* 



* Journal of Comparative Pathology and Therapeutics, vol. vi., 

 p. 195- 



