OSSEOUS TISSUE. 



851 



Fig. 453. 



The form* assumed by the bone cells in man. 

 Fig. 454. 



Various forms of bone cells found in the bone of the 

 Boa Constrictor. 



Fig. 455. 







a, form of bone cell in the common frog ; b, bone 

 cells from the crania of the common goldfinch ; 



c, form of bone cell in the sheep's-head fish ; 



d, form of bone cells in the green-boned fish. 



of any very definite enumeration, since no two 

 cells will be found possessed of a like number of 

 branching tubes. The general arrangement of the 

 tubes is radiate as regards the cells, which forms 

 their common centre. This statement requires 

 some qualification, for not uncommonly a much 

 greater number of tubes arise from one side of 

 the cell than from the other, and these tubes all 



take one direction. A tube after passing some 

 little distance from the cell will in many in- 

 stances divide, and each division pass on 

 distinct from its fellow, equalling in size the 

 parent tube. Frequent anastomoses are effected 

 between different tubes arising from the same 

 cells, but far more frequently between those 

 which arise from neighbouring cells. So fre- 

 quent are the connections that a free com- 

 munication is established between the various 

 cells and branching tubes throughout the 

 substance of the bone. 



So numerous are the connections between 

 the tubes, and immediately between the cells 

 through the tubes, that a fluid introduced into one 

 cell in a bone may find its way into every other 

 cell of the bone. Indeed this does take place, 

 though not from a single cell, yet from the 

 surface of the bone. If, for instance, you place 

 a bone that is dry, and opaque as a conse- 

 quence of being dry, in spirits of turpentine, in 

 a very little time this bone, before opaque, will 

 become comparatively transparent, and this 

 through the fluid having passed through the 

 tubes into the cells. For, as will be shown, it 

 is the tubes only that open upon the surface of 

 the bone, either the external surface or the sur- 

 face of the canals for vessels. Indeed, if a 

 thin section of bone be taken and all moisture 

 removed, and spirit of turpentine be added to 

 it, when under the microscope, the passage of 

 the fluid through the tubes may be seen, an ex- 

 periment suggested by my friend Mr. Bowman. 



Besides this relation between the tubes them- 

 selves and their cells, they have a very definite 

 relation to the Haversian canals as well as to the 

 free surface of the bone and also to the lamina?. 



The position occupied by the cells is between 

 the laminae, or on the surface of the laminae ; 

 and where concentric laminae occur, as in the 

 Haversian system, the cells are arranged in cir- 

 cular lines between the laminae, each line of cells 

 having as an exit common to it and the con- 

 necting laminae the Haversian canal. The 

 flattened sides of the cells are parallel with the 

 circumference of the Haversian canal, while 

 their greater diameter is in the direction of the 

 circular line of the lamina, or with the length 

 of the canal to which they belong. Bone 

 cells so placed send out numerous tubes, which 

 pierce the laminae at right angles and proceed in 

 great numbers to the vascular canal, into which 

 they enter, there terminating in an open mouth 

 upon the surface ; thereby establishing a con- 

 nection of tube channels between the bone cells 

 of the Haversian system and the canal of the 

 system. (See/zg.448.) Although these cells send 

 out many tubes in the above direction, yet others, 

 though comparatively few, take an opposite 

 course, and then establish by anastomosis a con- 

 nection with the tubes of the surrounding bone 

 cells. This is more particularly seen when we 

 look upon a transverse section of an Haversian 

 system; but if a section taken in the length of 

 an Haversian system be examined, the tubes 

 will for the most part be seen dividing the cells 

 equally in point of number from every part of 

 the circumference of the cell, and of course pro- 

 ceeding in the length of the laminae between 



3 i 2 



