bursa /bur″sə/ pl. bursae [Gk, byrsa, wineskin] , 1. a fibrous sac between certain tendons and the bones beneath them. Lined with a synovial membrane that secretes synovial fluid, the bursa acts as a small cushion that allows the tendon to move over the bone as it contracts and relaxes. Bursae may enlarge if subject to excessive forces, causing bursitis. See also adventitious bursa, bursa of Achilles, olecranon bursa, prepatellar bursa. 2. a sac or closed cavity. See also omental bursa, pharyngeal bursa.
