84 BO:SE. 



The cancellated texture has essentially the same lamellar structure. 

 The slender bony walls of its little cavities or areolae are made up of 

 superimposed lamellae, like those of the Haversian canals (fig;. 48 b, h), 

 only they have fewer lamellaj in proportion to the width of the cavities 

 which they surround ; and, indeed, the relative amount of solid matter 

 and open space constitutes, as already said, the only difference between 

 the two forms of bony tissue ; the intimate structure of the solid sub- 

 stance and the manner of its disposition round the cavities being- 

 essentially the same in both. 



Besides the openings of Haversian canals as above described, a trans- 

 verse section of the compact bone now and then presents vacuities or 

 spaces formed by absorption of the tissue. These are named " Haversian 

 spaces " by Tomes and De Morgan, who first showed that they occur 

 not only in growing bone but at all periods of life. In their primitive 

 condition these cavities are characterised by an irregular or eroded 

 outline, and their formation by absorption is further indicated by their 

 encroaching on the adjacent groups of concentric lamelke, which have 

 been, as it were, eaten away to a greater or less extent to give ]3lace to 

 the new cavity. In another stage the spaces in question are lined by 

 new-formed lamellae, which may as yet be confined to the peripheral 

 part of the vacuity, or may fill it up in a concentric series, leaving a 

 Haversian aperture in the middle, and in fact, constituting a system of 

 concentric Haversian lamellas, interpolated or intruded among those pre- 

 viously existing. The concentric lamellte, which thus come to occupy 

 a greater or less extent of the area of the cavity, are of course bounded 

 exteriorly by segments of adjoining sets of Haversian lamellEe, which 

 have been more or less cut in upon in the excavation of the space. It 

 has been further observed by Tomes and De Morgan, that vacuities 

 may sometimes be seen which are being filled up at one part by the 

 deposition of lamellre, whilst they are extending themselves by absorp- 

 tion at another. The Haversian spaces are most numerous in young and 

 growing bones ; but, as already stated, they occur also after growth is 

 completed. Their origin and changes Avill be better understood after the 

 reader has }ieruscd the account of the growth and development of bone, 

 to which head, indeed, the subject more properly belongs, although it 

 has seemed expedient to introduce it here. 



All over the section numerous little dark specks are seen among the 

 lamellae. These were named the " osseous corpuscles ; " but as it is now 

 known that they are in reality minute cavities existing in the bony sub- 

 stance, the name of lacunae has since been more fittingly applied to 

 them. To see the lacuniB properly, however, sections of unsoftened 

 bones must be prepared and ground very thin, and a magnifying power 

 of from 200 to 300 nmst be employed. Such a section, viewed with 

 transmitted light, has the appearance represented in fig. 49. The 

 openings of the Haversian canals are seen with their encircling lamellre, 

 and among these the corpuscles or lacuna3, which are mostly ranged in 

 a corresponding order, appear as black or dark brown and nearly 

 opaque oblong spots, with fine dark lines extending from them and 

 causmg them to loolc not unlike little black insects ; but when the 

 same section is seen against dark ground, with the light falling on it (as 

 we usually view an opaque object), the little bodies and lines appear 

 quite white, like figures drawn with chalk on a slate, and the inter- 

 mediate substance, being transparent, now appears dark. 



