Syndesmology is the study of ligaments. Ligaments are made of tough connective tissues and connect bone to bone. If this be examined with a rather low power the bone will be seen to be mapped out into a number of circular districts each consisting of a central hole surrounded by a number of concentric rings. These districts are termed Haversian systems; the central hole is an Haversian canal, and the rings are layers of bony tissue arranged concentrically around the central canal, and termed lamellæ. Moreover, on closer examination it will be found that between these lamellæ, and therefore also arranged concentrically around the central canal, are a number of little dark spots, the lacunæ, and that these lacunæ are connected with each other and with the central Haversian canal by a number of fine dark lines, which radiate like the spokes of a wheel and are called canaliculi. Filling in the irregular intervals which are left between these circular systems are other lamellæ, with their lacunæ and canaliculi running in various directions, but more or less curved (Fig. 73); they are termed interstitial lamellæ. Again, other lamellæ, found on the surface of the bone, are arranged parallel to its circumference; they are termed circumferential, or by some authors primary or fundamental lamellæ, to distinguish them from those laid down around the axes of the Haversian canals, which are then termed secondary or special lamellæ.