HISTOLOGY OF EPITHELIAL AND CONNECTIVE TISSUES. 41 



phate and carbonate are the most abundant. Immersed in dilute 

 solutions of hydrochloric acid, they can be converted into soluble 

 salts and dissolved out. The osseous matrix left behind is soft and 

 pliable. When boiled, it yields gelatin. 



A thin, transverse section of a decalcified bone, when examined 

 microscopically, reveals a number of small, round or oval openings, 

 which represent transverse sections of canals which run through 

 the bone, for the most part in a longitudinal direction, though fre- 

 quently anastomosing with one another. These so-called Haversian 

 canals in the living state contain blood-vessels and lymphatics. 



Around each Haversian canal is a series of concentric laminae, com- 

 posed of white fibers. Between every two laminae are found small 

 cavities (lacunae), from which radiate in all directions small canals 

 (canaliculi), which communicate freely with one another. The 

 Haversian canals, with their associated lacunae and canaliculi, form 

 a system of intercommunicating passages, through which lymph cir- 

 culates destined for the nourishment of bone. Each lacuna contains 

 the bone corpuscle, whicn bears a close resemblance to the usual 

 branched connective-tissue corpuscle, and whose function appears to 

 be the maintenance of the nutrition of the bone. 



The surface of every bone in the recent state is invested with a 

 fibrous membrane, the periosteum, except where it is covered with 

 cartilage. The inner surface of this membrane is loose in texture, 

 and supports a fine plexus of capillary blood-vessels and numerous 

 protoplasmic cells the osteoblasts. As this layer is directly con- 

 cerned in the formation of bone, it is spoken of as the osteogenetic 

 layer. 



A section of a bone shows that it is composed of two kinds of 

 tissue compact and cancellated. The compact is dense, resembling 

 ivory, and is found on the outer portion of the bone ; the cancellated 

 is spongy, and appears to be made up of thin, bony plates, which 

 intersect one another in all directions, and is found in greatest 

 abundance in the interior of the bones. The shaft of a long bone is 

 hollow. This central cavity, which extends from one end of the bone 

 to the other, as well as the interstices of the cancellated tissue, is 

 filled in the living state with marrow. The marrow or medulla is 

 composed of a connective-tissue framework supporting blood-vessels. 

 In its meshes are to be found characteristic bone cells or osteoblasts, 

 the function of which is supposed to be the formation of bone. In 

 the long bones the marrow is yellow, from the presence in the con- 



