these extensions are engageable by a key 58 fig5 for rotation of the rods to adjust the positions of the blades 42 and 44 threads 60 and 62 formed on the rods are threadingly engaged with internal threads formed in ring 40 which is fixed to both tubes a ball formed at the distal end of each rod fits between upper and lower plates formed on the blade with which the rod is associated at a location spaced a short distance from the pivot pin for example rod 50 is provided with a ball 64 and extends through a hole in upper plate 66 of blade 42 and fits in a space between the upper plate 66 and a lower plate 68 upon rotation of the rod in one direction the rod will pull up on plate 66 causing the blade 42 to pivot outward upon rotation of the rod in the opposite direction the rod will push on plate 68 causing the blade 42 to pivot inward the pitch of the threads of the threaded rods and the ring is preferably sufficiently small that the blades cannot be moved about their pivots by forces applied directly to the blades the balloon dissector 70 shown in fig7 comprises a second tube 72 the outer wall of which is preferably in the form of.