BONE 



75 



FIG. 88. ISOLATED BONE CELL, 

 SHRUNK AWAY FROM WALL 

 OF LACUNA AT I. 



(Schafer, after Joseph.) 



absorbed during the development of the bone. In a section through 

 the shaft of a long bone the Haversian systems are found in the middle of 

 the wall, while superficial to them and just within the periosteum are a 

 number of lamellae which may be traced 

 much or all of the way around the cir- 

 cumference of the cylindrical shaft, and 

 which are known as the external circum- 

 ferential or periosteal lamella. On the 

 inner surface of the compact bony wall is 

 a similar group of parallel laminae which 

 adjoin the marrow cavity, and are known 

 as the internal circumferential or endos- 

 teal lamellae. In their finer structure 

 the circumferential lamella? are exactly 

 similar to the cylindrical bony lamellae of 

 the Haversian systems. 



HAVERSIAN SYSTEM. A Haversian system contains a small central 

 canal (0.05-0.1 mm. dia.), which is occupied by connective tissue, marrow 

 cells derived from the marrow cavity during the process of development, 



small blood-vessels, nerve fibers, and 

 perivascular lymphatics. Concen- 

 trically arranged around the Haver- 

 sian canal are parallel layers of 

 dense fibrous tissue, the Haversian 

 lamellce. The fiber bundles of this 

 tissue form an interlacing network 

 whose bundles frequently cross each 

 other at right angles and whose in- 

 terstices are occupied by a solid cal- 

 careous mass, consisting chiefly of 

 the phosphates (about 80 per cent.) 

 and carbonates of calcium. From 

 four to twenty such calcareous lam- 

 ellae are found in each Haversian 

 system. The organic substance of 



bone consists chemically of collagen, osseomucoid and small amounts of 

 other albuminoid bodies. 



Both in and between the lamellae are many small ovoid spaces which 

 are partially filled by small flattened cells, the lone cells; these spaces 

 are known as the lacunce. From each lacuna minute canals, the canaliculi, 



FIG. 89. AN HAVERSIAN SYSTEM, 

 INCLUDING THE CENTRAL CANAL, 

 SEVERAL LAMELLAE, LACUNAE AND 

 CANALICULI. 



