29 L SPECIAL HISTOLOGY. 



§90. 



The matrix of bone is lamellar, and the lamellae (fig. 112) 

 are apparent in thin sections, but are still better shown in 

 bones from which the earthy matter has been removed, or 

 which have been exposed to the weather or calcined, in which 

 cases the lamellae exfoliate, and, in the cartilage of decalcified 

 bones, may even be raised with the forceeps. In the middle 

 portions of the cylindrical bones they constitute two systems — 

 one general, in which the lamellae are parallel with the external 

 and internal surfaces of the bone, and numerous special ones, 

 around the separate Haversian canals. These two systems are 

 in some places in immediate connection, but in most, merely 

 in apposition, and on that account they may conveniently be 

 regarded as of two kinds ; a view with respect to them, which 

 is in some degree supported by the phenomena presented in 

 their development. 



to the text. We may add, that although we do not always agree with Messrs. 

 Tomes and De Morgan in the interpretation of the facts, differences which we shall 

 duly note, our own investigations have led us to believe that their paper is by far the 

 most accurate account of the process of ossification which has yet appeared. 



These writers have pointed out the important fact, that besides the well-known 

 Haversian canals, other cavities exist in bone, which they denominate Haversian 

 spaces. These have irregular outlines similar to that of the surface of exfoliations, 

 while the boundaries of the Haversian canals are always more smooth and rounded. 

 Again, in the latter, the laminae are more or less conformable with the canal ; while 

 the walls of the spaces are formed by the unconformable edges and surfaces of the 

 laminae of the adjacent Haversian canals, which have, as it were, been eaten away to 

 form the space. In fact, bone, so far from being a permanent or stationary structure, 

 is continually being deposited, and as constantly re-absorbed. The Haversian spaces 

 are the result of the absorption of previously existing osseous tissue; but when this 

 process has gone on to a certain extent, deposition commences in the spaces, and 

 they are converted into Haversian canals. The calibre of these canals now becomes 

 narrowed up to a certain point by the continual laminar deposition of ossific matter; 

 which, after a while, is traversed by new absorptive tunnels, or Haversian spaces, and 

 is removed in its turn. 



The spaces are very numerous and large in newly-formed bone situated near 

 ossifying cartilage; while, in older bone, they are far less frequent and generally 

 smaller. They are, however, never absent ; being found even in old subjects. They 

 may be observed in various conditions in a series of sections. In one place the space 

 will have attained a large size, while in another part of the same section, its com- 

 mencement will be seen extending from one side of an Haversian canal. One side 

 of a space may be becoming the seat of a new system, while the opposite is under- 

 ig further enlargement. — Eds.] 



