270 SPECIAL HISTOLOGY. 



enter the compact substance, as at the points of insertion of many 

 tendons and ligaments, and beneath several muscles (temporal).* 



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 forceps. 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 pheno- 

 mena presented in their development. 



The lamellce of the Haversian canals (Fig. 112 c, 113 5) surround 

 those canals concentrically, in greater or less number. They consti- 

 tute, as it were, the walls of the canal, and are intimately united to each 



* [A most valuable contribution to our knowledge of the structure and development of 

 Bone has lately been made by Messrs. Tomes and De Morgan, in their " Observations on 

 the Structure of Bone," read before the Royal Society in June, 1852, but not yet published. 

 We are enabled, however, by the kindness of those gentlemen in allowing us to inspect 

 many of their preparations, and in furnishing us with the proofs of their paper, to make 

 some very important additions and corrections 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 Haver- 

 sian 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 con- 

 stantly 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 deposi- 

 tion 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 arid 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 commencement 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 undergoing further enlargement. TRS.] 



