1. An anomalous muscle belly of flexor digitorum superficialis (sublimis) presenting as an aching swelling and simulating a ganglion is reported.

2. It is suggested that this could be an atavastic muscle belly of flexor digitorum superficialis.

1. Four cases of spontaneous interosseous nerve palsy are reported.

2. The condition is commoner than is usually thought.

3. Recovery is quick after operation done to excise or exclude a band causing mechanical compression.