NAVICULAB DISEASE. 



343 



-\'ariety of changes, both within its interior and upon its articular 

 surface ; in one instance, to the deposition. of small calcareous 



^ Tio. 61 represents longitudinal sections o£,four navicular boncB, MtQ^ 

 tlirough their middle as near as possible. 



1. Healthy bone. Cancelli in their natural condition, ivith distinct 

 spaces (areola) between the bony trabeculae. 



2. Early stage of ostitis. The bone presents almost an ivory-1'ka^ 

 appearance, from exudation (and ossification of the exudate) into the 

 areolar spaces, rendering the bone almost solid. 



3. Second stage. Showing rarefaction of the bony tissue, and expan- 

 sion of the areolae ; the inflammatory new formation has been absorbed ; 

 the cancelli are enlarged, and cavities are formed (indicated by the dark 

 spots) by absorption of the bony trabecule. The exterior of this bono 

 shows no signs of disease. 



4. In this figure both the processes, viz., consolidation and rarefactioa^ 

 are going on. In the centre and to the left hand, dark spots (forammae) 

 are seen, indicating the destructive (raref active) process ; whilst to the right, 

 cmd indeed almost surrounding the cavities, the bone presents the ivory-like 

 appearance, the natural areolae being filled with bony matter. 2 and A 

 represent changes that are consonant. with those of rheumatoid disease. 



^pota upon and within the cartilage (see No. 2, Fig. 62); 



