BONE. 577 



and the intercellular substance, which was transparent 

 when viewed by transmitted light, is now perfectly dark. 



" Thus much may be said to compose the hard part of 

 the bone ; we must now turn our attention to the soft part. 

 This, as has been before stated, consists of the periosteum, 

 which invests the outer, and of the medullary membrane, 

 which invests the inner surface, lines the Haversian canals, 

 and is continued from them, through the canaliculi, into 

 the interior of the bone-cells ; and of the cartilaginous or 

 other matrix, which forms the investment of the minute 

 ossific granules. The earthy 

 matter of the bone may be 

 readily shown by macerating 

 the section for a short time 

 in a dilute solution of caustic 

 potash. 



" The animal matter may 

 be procured by using dilute 

 hydrochloric acid instead of 

 caustic potash; when all the 

 earthy matter is removed, 

 the section will exhibit nearly 

 the same form as when the 

 earthy constituent was pre- 

 sent; and if then viewed 



microscopically, it Will be Fig. 320.^f portion of the Cranium 



noticed that all the parts cha- of " S re " (Si " *<>) *e- 



. . markable for the large size of the 



racteriSing the Section pre- bone-cells and of the canaliculi, 

 vious to its rnarpratirm in thp which are larger in this animal than 



vioub to IDS maceration m tne in any other yet examined. AS in 



acid will be Still visible, but t ^ e preceding specimen, no Haver- 



not so distinct as when both sian canals ^ * resent - 

 constituents were in combination. When, however, the 

 animal matter is removed, the bone will not exhibit the 

 cells and the canaliculi, but is opaque and very brittle, 

 and nothing but the Haversian canals and a granular 

 structure can be seen. 



"If we consider what has been already mentioned as 

 entering into the composition of a bone, viz. the medullary 

 cavity, the Haversian canals, the canaliculi, and the bone- 

 cells, we shall find that every part described has been 

 more or less hollow; where, then, is the true bony sub- 

 p P 



