Abstract
1. Muscles acting upon any joint can be divided into two principal groups: muscles of displacement or spurt muscles, and muscles of stabilisation or shunt muscles.
2. Muscles which arise far from the joint are spurt muscles; those which arise near it are shunt muscles.
3. The fibrous tendon sheaths are joint-stabiising mechanisms.
4. The lumbrical and interosseous muscles are muscles of stabilisation of the digits.
5. The arrangement of the musculature is such as to ensure a constant pressure across the joint cavity during rest or uniform movement. The necessary centripetal force during movement is supplied mainly by the shunt muscles.
6. Experiments are described to illustrate these observations.