Synovial sheaths around the long tendons of the fingers.
A synovial sheath is a tubular bursa that surrounds a tendon. The tendon invaginates the bursa from one side so that the tendon becomes suspended within the bursa by a mesotendon. The mesotendon enables blood vessels to enter the tendon along its course. In certain situations, where the range of movement is extensive, the mesotendon disappears or remains in the form of narrow threads called the vincula. An example of this is the long flexor tendons of the fingers (see illustration) and toes.