The osteocytes extend their cell membranes and cytoplasm into these channels, and there the exchange is made. The picture below on the left is a close-up of the osteocytes with the radiating canaliculi. The picture on the right is an electron micrograph which illustrates the junction of two osteocytes in a canaliculi. Microscopic Structure of Spongy Bone Spongy bone does not have osteons, instead the bone tissue looks like a sponge - the bony pieces are called trabeculae, and they are arranged along the lines of greatest force to a bone, not haphazardly as you might think. The trabeculae are only a few cell layers thick and house the osteocytes, again connected by canaliculi.
Blood vessels run throughout the spongy bone, and marrow fills the spaces between the bone tissue.
The organic portion is composed of the collagen fibers secreted by the osteocytes and osteoblasts, and some glycoproteins. The organic portion of the matrix gives the bone strength and flexibility. The inorganic portion of the matrix is the hydroxyapatites, a fancy name for mineral salts. Calcium is one of the most important mineral, but you'll also find phosphorous, magnesium, and others. The mineral salts are deposited by the osteocytes around the collagen fibers.