TEXTURE OF BONES. 53 



surface of the other, and is composed of filaments and small 

 lamina?, which pass in every direction, by crossing, uniting, and 

 separating. The cells, resulting from this arrangement, pre- 

 sent a great diversity of form, size, and completion. They are 

 all filled with marrow, and communicate very freely with each 

 other. The latter may be proved in the boiled bone, by the 

 practicability of filling them all with quicksilver from any given 

 point ; and, indeed, by the injection of any matter sufficiently 

 fluid to run. The communications between them are formed 

 by deficiencies in their parietes, after the same manner that the 

 cells of sponge open into each other. This structure does not 

 exist in the earliest periods of ossification, when the bones are 

 cartilaginous almost entirely, but developes itself during the 

 deposite of calcareous matter. The manner of its formation 

 is imperfectly understood, though it may possibly be the result 

 of absorption, and it is not completed in the bones, originally 

 consisting of several pieces, till they are consolidated into one. 



The compact substance is also formed of filaments arid lami- 

 nae, which we find to be so closely in contact with each other, 

 that the intervals between them are merely microscopical in 

 the greater part of their extent: they become, however, more 

 and more distinct, and larger, near the internal surface; and at 

 the extremities of the long bones. The compact tissue is gra- 

 dually blended with the cellular structure, or lost in it. Its 

 filaments are directed longitudinally it) the cylindrical bones, 

 radiate from the centres of the fiat ones, and are blended so as 

 to render it impossible to trace them in the thick ones. This 

 disposition in the flat bones is much better seen in early life; 

 subsequently, it becomes indistinct. The compact tissue, par- 

 ticularly in the cylindrical bones, has in it a multitude of lon- 

 gitudinal canals, visible to the microscope, and some of them 

 to the naked eye, which contain vessels and medullary matter. 

 Those canals, originally described by Havers, are, according 

 to the estimate of M. Beclard, about one-twentieth of a line in 

 diameter, on an average; but they are, generally larger near 

 the interior than the exterior surface of the bones, and have 

 frequent lateral communications with the cellular structure, and 

 with the external surface. 



The compact and the cellular structures present themselves 



5* 



