MICROSCOPIC STRUCTURE OF BONES. 115 



through the substance of the bone ; around each of these 

 canals a series of bony laminae are concentrically arranged, 

 as if they resulted from rings of growth, and reminding 

 us of a transvere section of the branch of a dicotyledonous 

 tree. Between the laminae a number of peculiar spider-like 

 bodies are arranged likewise in a concentric manner ; they 

 have an irregular oval form, with jagged edges, and send 

 out from their circumference a number of small branching 

 tubes, which anastomose freely with the tubes from other cells, 

 forming thereby a complete network of tubes and reservoirs, 

 which traverse the osseous tissue in all directions. The sides 

 of the spider-like bodies lying nearest the Haversian canals, 

 send their small tubes to open into them, by which nutritive 

 fluids passing through the canals are absorbed and trans- 

 mitted through the osseous tissue, so that it is possible to inject 

 the spider-like bodies and the whole system of tubes, by forcing 

 fluids into any of the canals. The spider-like bodies have 

 received different names, as osseous corpuscles, calcigerous 

 cells, lacunae, or bone cells, according as the observer consi- 

 dered them to be solid or hollow. The spider-like bodies or 

 bone-cells in man, measure, on an average, about 1-1400 to 

 1 -2400th of an inch in their long diameter, and about from 

 1 -4000th to 1 -8000th of an inch in their shortest diameter. 

 The structure between the bone cells has been shewn by Mr. 

 Tomes* to consist of a cellular basis, in which the granular 

 earthy matter of bone is deposited. The granules vary from 

 l-6000th to the 1-14, 000th of an inch in size, and are best 

 shewn in a bone which has been long subjected to the 

 action of boiling water or steam. The microscope, there- 

 fore, enables us to demonstrate that bone is composed of 1st, 

 granular earthy matter, distributed throughout the cellular 

 tissue ; 2nd, bone cells and branching tubes, traversing the 

 osseous structure; the former being the hardening material ; 

 the latter for the distribution of nourishment through its 

 substance. This view of the function of the bone cells and 

 tubes is supported by the fact, that there is a constant relation 

 between the size of the bone cell and that of the blood cor- 

 puscle of the same animal, thus : 



In birds, a transverse section of the femur shews that the 

 Haversian canals are more numerous and smaller, and that 



* Cyclopaedia of Anatomy and Physiology. Art. Osseous Tissue, p. 843. 



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