CARIES. 167 



as the navicular, sesamoid, or bicipital groove of the humerus, 

 the fibres of the tendon become " ruptured by abrasion " upon the 

 roughened surface, or by an inflammatory softening — gelatina- 

 tion — of the tendon, whereby its smooth, cartilaginous surface 

 becomes roughened ; string-like processes of its fibres are seen 

 upon it; which finally unite to vascular projections from the 

 bone, and form a bond of union between the two. The pro- 

 gTess of caries is thus arrested by the adhesion of the tendon 

 to the bone. 



The effect of caries is to remove the bony laminal layer 

 and the cartilage, and thus destroy the articulation which it 

 may invade; but wliilst this process of destruction goes on 

 within the bone and upon its extremity, we find that the peri- 

 osteal surface and compact tissue become the seat of new bony 

 deposit, situated beneath the periosteum, which envelops the 

 diseased bone, as it were, in a ring, and extends to all the 

 bones of an articulation which may be involved in the caries ; 

 finally, binding them firmly together ; in fact, converting two or 

 more bones into one, and destroying motion. The united bones 

 now perform the functions of one bone ; and in virtue of this 

 the pain produced by the attrition of the roughened surfaces 

 of the bones one upon the other is no longer caused. 



Within the bone the degenerative process, in the majority of 

 cases that have been carefully examined by me, is limited by 

 consolidation of the cancelli ; and in a recent specimen which I 

 have in my possession, I found that the first alteration to be 

 observed, in addition to the increased vascularity, was the 

 removal of the fatty material — which is found abundantly in 

 bone during health — and the formation of an organizable lymph, 

 which is finally converted into bone, giving to the original 

 trabeculated structure an ivory-like appearance. 



The external signs of caries vary according to its seat. If it 

 be in the bones of an articulation having a distensible capsular 

 ligament, as the true hock, there will be swelling of the joint by 

 distension of its synovial membrane and capsular ligament, with 

 heat, pain, and lameness. But if it be limited to the mere gliding 

 articulations, their synovial membranes are too limited to allow 

 of this distension; and before the appearance of the external 

 subperiosteal deposition just referred to, the speciality of the 

 lameness and heat of the part are the only signs. 



