170 



DISEASES OF THE BONES AlH) ARTICULATIONS. 



of osseous matter takes place under the periosteum, and in 

 this manner the dead bone, which is 

 called a sequestrum, becomes enclosed 

 within a capsule, perforated by numer- 

 ous openings termed cloacae (see Fijj 

 25), and these are not filled up until 

 the dead bone is entirely i-emoved ; but, 

 after this has taken place, gi-anula- 

 tions spring up from the inner surface of 

 the shell, and the cavity is eventually 

 filled up by osseous matter, so that in- 

 stead of»al hollow bone we find a solid 

 cylinder. 



It may be~here noticed that the bones 

 of the legs of race-horses are more liable 

 to necrosis than those of animals of a 

 coarser breed, not only because they are 

 subjected to greater concussion, but being 

 more compact in their structui-e, inflam- 

 mation in them is apt to terminate in 

 their death. 



The separation of the sequestrum is de- 

 scribed as follows by Rokitansky : — " All 

 round the necrosed portion, that is to 

 say, at its margins, and at the part where 

 its surface is exposed to that of the healthy 

 Fio. 25.— NecrosiB totalis bone, the latter underjToes a gradual ex- 



of metatarsal bone, a, Se- . . . ° „ . . 



questrai capsule, b and c, pansion or rarefaction of its tissue, by 

 Cloaca, or foramina grandia. ^j^^ enlargement of its Haversian canals, 

 assumes a rosy colour, and becomes succulent. It gradually 

 acquires an areolar structure, and is thus more rarefied ; 

 at length it disappears altogether, and a red, soft, spongy 

 substance, or layer of granulations, occupies its place. This 

 change is produced by the inflammatory process, which gives rise 

 to suppuration and granulation ; the bony tissue beginning witli 

 the Havei-sian canals is dis.solved by the matter secreted witliin 

 them ; while the granulations which shoot fortli at the same 

 time fill up the enlarged canals. The immediate result of this 

 process is the formation of a furrow of demarcation, which en- 

 circles the margin of the dead bone, asd is filled up with granula- 



