A device for enabling sequential dilation of a percutaneous tissue opening to seccessively larger opening sizes. The device includes a first-elongated dilator element having a forward end, an intermediate dilator body and a tail section extending from shoulder structure at the junction of the intermediate...http://www.google.com.au/patents/US4862891?utm_source=gb-gplus-sharePatent US4862891 - Device for sequential percutaneous dilation
