114 LOCOMOTION. [CHAP. v. 



remarkable circumstance,, and will be illustrated when we come to 

 speak of the development of bone. 



The lamellated character of bone can be frequently distinguished 

 in the periosteal, medullary, and Haversian layers ; and, in general, 

 wherever several successive series of lacunae exist. The Haversian 

 rods, however, are remarkably prone to exhibit this appearance, 

 Fig. 27. especially under the condi- 



tions previously mentioned 

 (p. 111). Their lamellae, how- 

 ever, are not concentric, as 

 commonly described. The 

 fissures which disclose them 

 are indeed concentric, but 

 they are always incomplete, 

 never extending completely 

 round the canal ; so that the 



Transverse section of the compact tissue of a tibia from in , ,1 



an aged subject, treated with acid; shewing the appearance Iamell83 run into OUC anotlier 



of lamellae surrounding the Haversian canals. Portions of , mi 



several systems of lamella are seen. The appearance of the at VariOUS points. llllS re- 



lacunse, when their pores are filled with fluid, is also seen, -i, /> ,-1 / , ,-t , ,-1 



as well as the radiation from the canals which then remains. SUltS ITOm TIlC laCt, tnat me 



From Mr. Tomes. i T 



lacunae are not arranged in 



sets equidistant" from the centre, but are scattered, as it were, inde- 

 pendently of one another, at every possible variety of distance from 

 the canal (figs. 23 and 27). The larger concentric cracks, which 

 generally run through the lacunae, seem to occur where two or 

 three of these happen to lie nearly in the same curve. Bone is 

 very apt to crack in the interval between the rods ; and each of 

 these rods is really, so distinct from those near it, that it may be 

 designated conveniently, for the purposes of description, as an 

 Haversian system of lamella. 



In a longitudinal section of the compact tissue of a long bone 

 (fig. 19, p. 107) the appearance of lamellation is generally less evi- 

 dent, except where a longitudinal canal happens to lie exactly in the 

 plane of section. When the Haversian canal is a little below the 

 cut surface, it is of course covered by some of its lamellae, the 

 lacunae of which directly over it are seen in face, while the 

 lamellae dipping in on either side, in their course round the canal, 

 present the thin edges of their lacunae to the observer. In the 

 former part those pores alone are seen that proceed from the edge 

 of the lacunae ; while in the latter those from both surfaces are seen, 

 and of course appear much more numerous. 



The description now given of the intimate texture of the com- 

 pact tissue of long and short bones will apply, in all essenti 



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