FORMATION OF THE TISSUES BONE. 



483 



Haversian canals, seen on a lon- 

 gitudinal section of the compact tis- 

 sue of the shaft of one of the long 

 bones; 1, arterial canal ; 2, venous 

 canal; 3, dilatation of another ve- 

 nous canal.] 



change appears to be constantly taking place, [Fig. 116. 



perhaps for the purpose of keeping the Bone- 

 producing apparatus in a state fit for use, against 



the time when its actions may be needed, to repair 



the effects of injury or disease. Although a large 



quantity of blood is sent to Bone, the vessels do not 



penetrate its minute parts ; being confined to the 



Medullary cavity, and to the Haversian canals and 



Cancelli which are prolongations of it. Hence, as 



the density of Bone does not allow fluid to transude 



its substance in the manner of Cartilage, the ne- 

 cessity for some channel of nutritive matter is easily 



to be understood. It may be desirable to mention 



that the cavities and tubuli have been supposed, 



on account of the black appearance they exhibit 



under the microscope, to be filled with opaque 



matter ; but this appearance is common to all ca- 

 vities excavated in a highly-refracting substance 



(being shown by a bubble of air in Water), and 



ceases when a very thin section is examined, espe- 

 cially if it have been placed in Canada Balsam. 



In the bones of Mummies, they are found to be 



filled with a waxen material ; by which their power 



of imbibing fluid substances is clearly proved.* 



The ultimate substance of Bone appears to be 



usually granular ; the granules are stated by Mr. 



Tomest to be often very distinctly visible, without any artificial preparation, 



in the substance of the delicate spicula of the cancelli, when viewed with a 

 high power ; and to be made very evident by prolonged boiling in a Papin's 

 digester. They vary in size from l-6000th to l-14,000th of an inch ; their 

 shape is oval or oblong, often angular ; and they cohere firmly together, pos- 

 sibly by the medium of some second substance. A somewhat fibrous structure, 

 however, resembling that of the second class of Cartilages, sometimes presents 

 itself ; and this is especially the case in Cartilages ossified late in life, as those 

 of the ribs, larynx, &c. 



630. As to the mode in which Bone is produced from Cartilage, great 

 difference of opinion has prevailed : and 

 the question cannot be regarded as yet by 

 any means thoroughly elucidated. By 

 some it has been maintained that the cor- 

 puscles or cells of Cartilage become the 

 stellate cavities of bone ; and that the 

 intercellular substance of the one remains 

 in the other ; although consolidated by 

 the deposit of mineral matter. A careful 

 examination of the process of transforma- 

 tion, however, makes it appear that, in 

 Cartilage which is undergoing ossifica- 

 tion, the cells are arranged in linear series 

 of twenty or thirty ; and that the spaces 

 occupied by these ultimately become the 

 cancelli and Haversian canals. In the 

 thin lamellae of intercellular substance, by 



[Fig. 117. 



Scapula of a Foetus at the seventh month; 

 showing the progress of ossification. Natural 

 size. The light parts are epiphyses as yet car- 



tilaginous. From the Museum of King's Col- 

 lege, London.] 



Smee, loc. tit. 



f Todd and Bowman's Physiological Anatomy, p. 108. 



