852 



OSSEOUS TISSUE. 



which the cell is placed. As in the transverse 

 section of the Haversian system these tubes 

 that take the longitudinal direction are not 

 seen, so in this section the tubes proceeding 

 directly towards the Haversian canal are but 

 badly shown. So many of the delicate tubes 

 take the direction of the Haversian canals and 

 enter it, that the parietes of each canal at first 

 sight have a radiate appearance, which has led 

 some writers to describe a system of radiate 

 tubes passing through some of the laminae, but 

 they have failed to trace their connection 

 with the bone cells not far distant. When the 

 cell with its radiating system of tubes is situated 

 near the surface of the bone, the direction of 

 the latter will be mostly towards that surface, 

 unless indeed there is a vascular canal near at 

 hand, in which case many will proceed towards it. 

 Those cells which are placed in the connect- 

 ing lamince send out their tubes tolerably 

 equally in each division, anastomosing freely 

 with the tubes coming from the cells belonging 

 to the Haversian or superficial system of laminae, 

 and so establish a communication between the 

 cells of the three systems of laminae. The 

 number of tubes and the size of the bone cells 

 bear to each other no definite proportion ; thus 

 a small cell may have many tubes while a much 

 larger one has comparatively few. The number 

 of the cells in a given space is subject to con- 

 siderable variety, as well as the number of the 

 radiating tubes, though generally the number of 

 tubes will exist in inverse proportion to the num- 

 ber of the cells. Thus in the crania of small 

 birds the cells are of very frequent occurrence, 

 while the tubes connected with each cell are but 



Fig. 456. 



Sec/inn of a bone of an osseous fish. 



a, transverse section of Haversian canal ; b, longitudinal 

 section of an Haversiaa canal with system of tubes opening 

 into it. 



few. Again, in dense bones of quadrupeds and 

 of man, the cells are less frequent, but the tubes 

 of each cell far more numerous. 



Where the canals for vessels are very nu- 

 merous the bone cells become more rare, and 

 in some cases they are nearly absent,as shown in 

 Jig. 451. 



From the foregoing description it may be 

 seen that the infinitely numerous tubes every- 

 where connected amongst the cells, converging 

 at certain points and entering into cells, in fact 

 form these cells ; that the cells are nothing more 

 than many tubes coming to a point and losing 

 their individual parietes. 



In other cases where the tubes to each cell 

 are not numerous, the cell itself may be com- 

 pared to a dilatation of those tubes. This view 

 of the subject is borne out by the fact that even 

 in the human subject we find here and there 

 tubes occupying the place of the cells and 

 their radiating tubes, while in certain fish the 

 cells are almost entirely absent and the simple 

 tubes general. 



In such instances the tubes hold the same 

 relation to the Haversian canals as do the bone 

 cells where they exist. (See Jig. 456.) 



The cells when seen by transmitted light, espe- 

 cially in a transverse section of bone, appear 

 perfectly opaque ; this has given rise to the 

 opinion that they contain some amorphous salt, 

 and the fact that these same cells become trans- 

 parent when the bone has been subjected to the 

 action of acid, confirmed observers in this 

 opinion, and that this salt was a salt of lime. 

 When first these observations were commenced 

 I was disposed to hold a like opinion, but fur- 

 therinvestigation has convinced me thatasa rule 

 the cells are empty. I have seen, and that too 

 very frequently, cells which were ob- 

 viously without contents, and this 

 observation may be repeated in any 

 bone where the cells are tolerably 

 large by making a section in the 

 length of bone, and so parallel with 

 the direction of most of the Haversian 

 canals. By making such a section 

 you expose the cells in their largest 

 diameter, when they maybe seen into ; 

 whereas if cut through in their narrow 

 diameter they are so deep that they 

 produce complete interference of light, 

 and so seem black, as though filled 

 with some opaque substance. 



Again, if turpentine or thin Canada 

 balsam be added to a section quite 

 dry beforehand, the dark cells will 

 become filled with turpentine or bal- 

 sarn, and so become transparent. 



The function performed by the bone 

 cells is no doubt that of circulation. 

 Atmospheric pressure would prevent 

 them from remaining empty, and as 

 their openings are always upon a 

 surface where there are bloodvessels, 

 the fluid portion of the blood is pro- 

 bably carried into them. Supposing 

 them oncefilledwith liquor sanguinis, 



the varying density of the blood itself 

 would produce a slow kind of circu- 



