Chap. III.] 



BONE. 



21 



cells which lie in cell-spaces or cavities called lacunce, and run- 

 ninof ont in a wheel-like or radial direction from each lacuna 

 are numerous tiny canals or canaliculi connecting one cell-space 

 or lacuna with another, and forming a system of minute inter- 

 communicating channels. 



All bones are covered by a vascular fibrous membrane, the 

 periosteum, and, unlike cartilage, the bones are plentifully sup- 

 plied with blood. If 

 we strip this perios- 

 teum from a fresh 

 bone, we see many 

 bleeding points repre- 

 senting the apertures 

 through which the 

 blood-vessels enter the 

 bone. After entering, 

 the blood runs through 

 short longitudinal 

 channels which com- 

 municate freely with 

 one another, and are 

 called, from the name 

 of their discoverer, 

 Haversian canals. 

 Around these Haver- 

 sian canals, as we have 

 already stated, the la- 

 mellae are disposed in 

 rings, while the lacunae 

 containing the bone- 

 cells are also arranged, 

 between the lamellce, 

 in circles around the 

 canals. As the canaliculi run in a radial direction from the 

 lacunce across the lamellse, it follows that the innermost ones 

 must run into the Haversian canals, so that there is a direct 

 communication between the blood in these canals and the cells 

 in all the lacunse connected with and surrounding each Haver- 

 sian canal. In this way the whole substance of the bone is 

 penetrated by intercommunicating channels, and nutrient mat- 



FiG. 14. — Transverse Section of Compact 

 Tissue (of Humerus). (Masnified about 150 diam- 

 eters.) (Sharpey.) Three of the Haversian canals 

 are seen, with their concentric rings faintly indi- 

 cated ; also the lacunae, with the canaliculi extend- 

 ing from them across the direction of the encircling 

 lamellse, or concentric rings. 



