BONE. 67 



Although, for the most part, the intercellular sub- 

 stance of bone is, by the ordinary modes of prepara- 

 tion, apparently quite destitute of structure beyond 

 that indicated by its lamellation, we yet find in 

 certain portions a well-defined system of fibres. 

 If, in a decalcified bone, some of the external la- 

 mellae are torn off, numerous fine, fibrillated, spicula- 

 like projections are seen hanging on to the inner 

 surface of the separated fragments. These are the 

 so-called Sharpey s fibres, which, passing inward from 

 the periosteum, pierce the bone either obliquely or 

 at right angles. As we shall see when studying the 

 development of bone, these Sharpey's fibres are the 

 remains of fibrillated connective -tissue bundles, 

 which originally occupied the situation now filled 

 by bone. Recent investigations, moreover, have 

 led to the belief that in bone, as in hyaline cartilage, 

 the basement substance is everywhere delicately 

 fibrillated, but we have not space in this manual to 

 consider the methods by which this may be demon- 

 strated. 



2. Periosteum^ The periosteum consists chiefly 

 of fibrillated connective tissue, with a few elastic 

 fibres, and we recognize in it two layers : an outer 

 layer, composed chiefly of firm, dense connective 

 tissue, which is continuous with the muscular apo- 

 neuroses surrounding the bone ; and an inner layer, 

 which is looser in texture, more vascular, and abun- 

 dantly furnished with variously shaped cells. The 



