SECT. 27.] 



OSSEOUS TISSUE. 



6l 



Fig. 23. 



Haversian canals, which open abundantly on the outer and inner 

 surfaces of the bones. 



The matrix of bones consists of an intimate mixture of an or- 

 ganic substance, agreeing entirely in nature with that of connective 

 tissue, and certain inorganic constituents, of which the phosphate 

 and carbonate of lime form the principal part. The fluid contained 

 in the lacunas and canaliculi is not accurately known ; but it pro- 

 bably chiefly contains albumen, fat, and salts, like the blood-plasma. 

 By their firmness and hardness, the bones serve to support the soft 

 parts, and to enclose and protect them. They occasionally, also, 

 fulfil special ends, as, for example, the auditory ossicles and the 

 parts of the labyrinth which conduct 

 the waves of sound. 



The development of bone takes place 

 in two modes : first, bv the metamor- 

 phosis of true cartilage; and secondly, 

 by that of ordinary connective tissue. In 

 both cases, the cells are converted into 

 lacuna : in theformer, the cartilage-cells; 

 in the latter, the plasm-cells ; and this 

 takes place after two somewhat different 

 types. "When cartilage ossifies, the 

 cartilage-cells, produce a new gene- 

 ration of soft cells and these only 

 assuming a stellated form, are trans- 

 formed into lacunae. On the other hand, 



d 



when connective tissue ossifies, its cells 

 undergo no greater changes ; that is to 

 sav, while the fibrous substance of the 

 connective tissue takes up calcareous 

 salts, the cells grow out in a stellate 

 manner and anastomose, or when they 

 pre-existed as stellate anastomosing 

 plasm-cells, simply i*emain as such. 

 Thus the lacuna of bone are in evert) 

 case cells, and, accordingly, would be 

 better denominated bone-cells. In all 

 bones, as Virchow first discovered, 

 these bone-cells can be readily isolated 

 by maceration in acids and alkalies, as 

 well as by boiling. The matrix of the 

 bones arises, in the one case, by the 



1 M &>■- " 



M. 



From the inner surface of the parietal 

 bone of a new-born child ; magnified 300 

 times, a. Bone with lacunae still pale 

 and soft. b. Border of the same. c. 

 Ossifying blastema, with its fibres and 

 cells. B. Three of these cells, magnified 

 350 times. 



