BONE. 296 



The fact of the free communication of the medullary cells 

 is proved by the two following experiments : 



Thus, when mercury is poured into a hole made in the 

 extremity of a long bone, or on the surface of a flat or 

 short one, it will traverse all the medullary cells, and escape 

 by the apertures which exist naturally on the exterior of 

 bones. 



Again, if a bone be cut through at one of its extremities, 

 the natural openings on its surface being at the same time 

 closed, and if then the bone be exposed to the action of 

 heat, all the marrow will escape slowly by the cut ex- 

 tremity. * 



The spaces described by the medullary cells are irregular 

 in size and form, those which are first developed being 

 smaller than those of older formation (see Plate XXXIV. 

 Jig. 3, 4.) : they are usually of an elongated shape, their long 

 axes being parallel to that of the bone itself: when viewed 

 transversely, they are seen to be more or less rounded, but 

 irregular in outline : it is in the transverse sections that the 

 bone cells and lamellae are best seen. 



Medullary cells in the recent state are filled with fat 

 vesicles, with blood-vessels, and with granular nucleated cells 

 analogous to those of epithelium : these last occur in con- 

 siderable quantities in the cancelli, and especially in those of 

 foetal bones, in which the fat vesicles are for the most part 

 absent. (See Plate XXX. fig. 4.) 



They inosculate freely with the medullary canals situated 

 in the outer and compact plates of bone. 



Canalicular Structure. 



The compact tissue of bones is traversed by canals, which 

 have been termed medullary from the fact of their being in 

 communication in the long bones with the great central 

 medullary cavity, and from the circumstance of their being 



* Bichat, Anatomic Generate, t. 111. p. 25. 

 B B 



