The osteocytes are directly connected to other osteocytes, surface lining cells and less directly to the blood vessels and nerves coursing through the Haversian and Volkmann's canals. They become parts of the bone's 3-D osteointernet ( Burger, 2001 ; . Martin et al., 1998 ; Moss and Cowin, 1997 ; L. Wang et al., 2000 ) ( fig. 2 ). They live in tiny cells called lacunae and extend processes through narrow canals known as canaliculi to plug directly into the other members of the internet with so-called gap junctions, which by directly joining the cells' cytoplasms form the "internal pathway" ( fig. 2 ). (Wonderful methacrylate-divinlybenzene replicas of the awesomely interlacing lacunocanalicular network of a mandibular bone's osteointernet can be seen in Figures 6a,b of Atkinson and Hallsworth (1983) ). The canaliculi end in tiny openings or ports in the lining cell-covered osteonal wall, and the processes may set up gap junctions with the lining cells. High molecular weight nutrients from the osteonal blood vessels are pushed through the ports and along the extracellular channel, the "external pathway", in the canaliculi, and wastes are sucked out of them into the osteonal lumen and ultimately the blood by the cycles of compression and expansion of the network during various body movements ( Knothe-Tate, 2001 , 2003 ; L. Wang et al., 2000 ) ( fig. 2 ). In trabecular bone, the canalicular ports also open onto lining cell layers, but these lie directly on the vascular elements (sinusoids) of the bone marrow, which are the equivalents of the blood vessels of the cortical bone's osteonal plumbing system except any injected agent, such as a growth factor or hormone, arrives there before the osteonal plumbing (., Knothe-Tate, 2001 , 2003 ; L. Wang et al., 2000 ).