Canaliculi are microscopic canals between the various lacunae

Lacuna (histology)

In histology, a lacuna is a small space containing an osteocyte in bone or chondrocyte in cartilage.-Bone:The Lacuna are situated between the lamella, and consist of a number of oblong spaces. In an ordinary microscopic section, viewed by transmitted light, they appear as fusiform opaque spots...

 of ossified bone

Bone

Bones are rigid organs that constitute part of the endoskeleton of vertebrates. They support, and protect the various organs of the body, produce red and white blood cells and store minerals. Bone tissue is a type of dense connective tissue...

. The radiating processes of the osteocytes project into these canals. These cytoplasmic processes are joined together by gap junction

Gap junction

A gap junction or nexus is a specialized intercellular connection between a multitude of animal cell-types. It directly connects the cytoplasm of two cells, which allows various molecules and ions to pass freely between cells....

s. Osteocyte

Osteocyte

An osteocyte, a star-shaped cell, is the most abundant cell found in compact bone. Cells contain a nucleus and a thin ring of cytoplasm. When osteoblasts become trapped in the matrix they secrete, they become osteocytes...

s do not entirely fill up the canaliculi. The remaining space is known as the periosteocytic space, which is filled with periosteocytic fluid. This fluid contains substances too large to be transported through the gap junctions that connect the osteocytes, including calcium

Calcium

Calcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft gray alkaline earth metal, and is the fifth-most-abundant element by mass in the Earth's crust...

 and phosphate

Phosphate

A phosphate, an inorganic chemical, is a salt of phosphoric acid. In organic chemistry, a phosphate, or organophosphate, is an ester of phosphoric acid. Organic phosphates are important in biochemistry and biogeochemistry or ecology. Inorganic phosphates are mined to obtain phosphorus for use in...

 ions.

In cartilage

Cartilage

Cartilage is a flexible connective tissue found in many areas in the bodies of humans and other animals, including the joints between bones, the rib cage, the ear, the nose, the elbow, the knee, the ankle, the bronchial tubes and the intervertebral discs...

, the lacunae and hence, the chondrocytes, are isolated from each other. Materials picked up by osteocytes adjacent to blood vessels, are distributed throughout the bone matrix via the canaliculi.