Muscles are attached to bones either directly by their fleshy fibres or by tendons which proceed from them. Tendons transmit the action of muscles to the bones to be acted upon. They exist in the form of dense rounded cords of various lengths, or as more or less broad, flat, expanded sheets. In the latter condition they are spoken of as aponeurotic tendons, and are found in their highest development in connection with the muscles of the belly, where they assist in forming the abdominal walls. The long cord like variety are met with in the extremities, where the more important extend from above the knees and hocks downward to the feet and pasterns.
Some tendons are partly or completely surrounded by a fibrous sheath, and this is lined by a synovial membrane, which, being also reflected on to the tendon, enables the latter to move freely through the former. This is more especially the case in the vicinity of joints, as the knee, hock, and fetlock, where movement is most active. Where tendons play over projecting points of bone or other prominences, a small, round sac lined with synovial membrane is placed between them to facilitate the movement of the one over the other. These are known as synovial bursae.