BONE TISSUE. 63 



resistance here imposes a veto to the circulation which is with 

 difficulty removed. 



Are the lacunae and calcareous canals only cavernous sys- 

 tems excavated in the hard, solid basis substance, or have 

 they a special parietes ? After energetic macerating media, 

 the previously decalcified bone presents a thin resistant 

 boundary layer around the lacunae and canaliculi. It appears 

 to be a decalcified elastic substance. It was formerly errone- 

 ously considered to be a cell membrane. 



Having become familiar with the most essential portion of 

 the structure in the diaphysis, let us now turn to a very short 

 discussion of the other parts of the skeleton. The beauti- 

 ful regularity here disappears, sometimes to a less, sometimes 

 to a greater degree. Even in the epiphyses of the cylindrical 

 bones, in consequence of the thinness of the osteoid plates, 

 the systems of lamellae are present in a far less developed 

 condition around the Haversian canals, and the inner funda- 

 mental lamellae are absent. In spongy' bone tissue the 

 laminar arrangement may still be distinctly recognized in the 

 thick trabeculae and plates, while it disappears more and 

 more with the decrease in size. In the cortical layers of flat 

 bones, the medullary canals run parallel to the surface, gene- 

 rally starting from a point and assuming a radiate direction. 

 In the short bones the course generally preponderates in one 

 direction. Funnel-shaped apertures of the Haversian canali- 

 culi may join together and form small medullary cavities, the 

 prefigurations of the larger, etc. 



The bones contain but little water, the compact having 3 to 

 7, the spongy 12 to 30 per cent. The organic, form-deter- 

 mining basis, amounting from 30 to 45 per cent, in the dry 

 bone, is transformed by boiling into glutin, that is, the ordi- 

 nary glue of the connective tissue. This is diffusely hardened 

 by the embedded bone earths. By this is understood a mix- 

 ture, amounting from 51 to 60 per cent., of lime salts with a 

 slight admixture of magnesia salts. The bone earths yield 

 about 86 per cent, of phosphoric acid, 9 of carbonate of lime, 

 3.5 of fluoride of calcium, and 2 of phosphate of magnesia. 



