An anal retractor includes four retractor valves (48), which are offset 90° relative to each other and can be moved radially apart from each other. For this the four retractor valves (48) are guided by sleds (30) in radial guide slots (14) of a base plate (10). For movement of the sleds (30) guide bolts...http://www.google.co.uk/patents/US7182730?utm_source=gb-gplus-sharePatent US7182730 - Anal retractor
