74 SKELETON. 



nium there is rather a tendency to the absorption of the diploe, 

 and the approximation of their tables. 



The bones, also, become more brittle in old age, in conse- 

 qneuce of the increase of calcareous, with a diminution of 

 gelatinous matter. The reverse being the case in infancy, 

 they are more flexible than in the adult, and can even bear to 

 be twisted or bent without breaking.* 



SECT. III. ON THE FORMATION OF CALLUS. 



As this is a consequence of bones being fractured, and a mode 

 that nature takes to repair the accident, there is some resem- 

 blance between it and the primitive formation of bone. Owing 

 to the rupture of the blood vessels of the bone; of those of the pe- 

 riosteum, and of the medullary membrane; and frequently of the 

 vessels of contiguous parts, the first effect of the accident is an 

 effusion of blood into the cavity of the fracture. The several 

 contiguous soft parts then swell, become hardened and inflamed; 

 and, in the mean time, an absorption of the blood is proceeding, 

 while an effusion of coagulating lymph from the ruptured ves- 

 sels occurs in the cavity of the fracture. A ring, the thickest 

 part of which is precisely over the seat of the fracture, is formed 

 by the lacerated parts ossifying: there is also formed in the in- 

 terior of the bone a sort of osseous pin. Till this moment the 

 bone itself remains unchanged, with the exception of a coating 

 of coagulating lymph on its broken faces; but now its extremi- 

 ties begin to coalesce or fuse themselves into each other, the su- 



*The reported instances are now numerous, where, from a defective organiza- 

 tion of bone, fracture is produced from very trivial causes; and this state is not 

 confined to any particular age, for it extends from infancy to advanced life. I 

 have attended a fractured os femoris in a child of two years, from a stumble in 

 walking across a carpeted floor. In another child the os femoris was broken, so 

 far as could be learned, by the nurse stooping to reach something from the floor: 

 the same child had both clavicles broken, without any one knowing when or 

 where: the left side was flattened, from the fracture, probably a partial one, of 

 several ribs, equally inexplicable. In a third child the tibia was broken from a 

 trifling fall on the floor, and the clavicle from striking the shoulder moderately 

 against the rounded back of a chair. 



In these several instances the fragility may arise cither from a defective rela- 

 tion of the constituents of the bone to each other, by a deficiency of animal mat- 

 ter, which diminishes the tenacity of the bone, or it may arise from attenuation 

 merely of the bone, leaving its points too thin for ordinary accidents. 



