164 



ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC. 



3 



of bone. It is not to be imagined, however, that blood can be conveyed by 



these tubuli, their size being far too small ; for 

 [Fig. 05. their diameter, at their largest part, is estimated at 



from 1-1 4,000th to l-20,000th of an inch, whilst 

 that of the smaller branches is from l-40,000th to 

 1-60, 000th of an inch ; so that the blood-corpus- 

 cles could not possibly enter them. But it may be 

 surmised that they draw fluid from the nearest 

 blood-vessels, and thus keep up a sort of circulation 

 through the osseous substance, which may con- 

 tribute to its growth, and may keep it in a state fit 

 for repairing itself, when injured by disease or vio- 

 lence. The lacunae, however, do not seem to be 

 unoccupied in the living bone ; for each contains 

 (according to Mr. J. Goodsir) a minute granular 

 substance, which seems to be identical with the 

 nucleus of the original bone-cell, and which pro- 

 bably serves as a " nutritive centre," attracting to 

 itself, through its own system of canaliculi, the 

 nutritive materials supplied by the blood-vessels of 

 the nearest surface, and diffusing these through the 

 surrounding substance.* 



canals, seen on a 195, Although a large quantity of blood is sent 

 longiiudmai section of the com- to B one? the vessels do not penetrate its minute 

 pact tissue of the shaft of one of being confined to the Medullary cavity, 



the longbones: 1, arterial canal; . . "= _ . . _ /. . . ' 



2, venous canal ; 3, dilatation of and to the Haversian Canals, and Cancelli, which 

 another venous canal.] are prolongations of it. The substance oi the Bone, 



therefore, is really as non-vascular as that of Carti- 

 lage ; the only difference being, that it is channelled out by more numerous 

 inflexions of the external surface, and that the vessels are thus brought into 

 nearer proximity with its several parts. The delicate osseous lamellae, which 

 form the walls of the cancelli, and of the large cells excavated in some of the 

 cranial bones, have a structure precisely analogous to that of the cylindrical 

 laminae surrounding the Haversian canals of the long bones ; and derive their 

 nourishment from the vascular membrane covering their surface, through the 

 medium of a similar set of lacunas and canaliculi. They do not themselves 

 contain Haversian canals or cancelli ; because no part of their substance is far 

 removed from a vascular membrane. The cylindrical rods, that make up the 

 hollow shaft of a long bone, are connected together by solid osseous sub- 

 stance, which is composed of lamellae running parallel to the external surface 

 of the bone; and these derive their nutriment either from the periosteum, or 

 from the membrane lining the great central medullary cavity ; according as 

 they are nearest to one or to the other. The membranous lining of the canals 

 of Bone appears to be supplied with lymphatics, and also with nerves ; but 

 with both in a very limited amount. The periosteum seems to be scarcely 

 (if at all) sensible in the state of health, although painfully so when inflamed ; 

 and the same may be said of the membrane lining the Haversian canals and 

 cancelli. The membrane lining the central medullary cavity, however, is more 



' The lacunae and canaliculi of Bone were formerly supposed, on account of the black 

 appearance they exhibit under the Microscope, to be filled with opaque matter; but this ap- 

 pearance is common to all cavities excavated in a highly-refracting substance (being shown 

 by a bubble of air in water), and ceases when a very thin section of Bone is examined, es- 

 pecially if it have been placed in Canada Balsam. In the Bones of Mummies, they are found 

 to be filled with a waxen material ; and in those which have lain in bogs, they are rendered 

 peculiarly distinct by the infiltration of some of the surrounding black matter: so that their 

 power of imbibing liquids is clearly proved. 



