In a further preferred aspect of the present invention, the elongate penetrating element is a needle, having {HEAD ~ a retractable obturator} at {TAIL ~ its distal end} 
at
In a further preferred aspect of the present invention , the elongate penetrating element is a needle , having { HEAD ~ a retractable obturator } at { TAIL ~ its distal end }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL