housing and reciprocates into the cannula housing when a proximally directed force is applied thereto the piercing tip is maintained in the exposed position by a latching mechanism associated with the obturator shaft and is automatically withdrawn into the cannula under the force of a spring when the proximal force is removed from the cannula the cannula thus advancing distally and releasing the latching mechanism penetration force is maintained at a minimum and safe and efficacious trocar entry is facilitated application_number US 35227494 A description referring to fig1 trocar 10 is shown in its fully assembled condition with cutting tip 12 extending from cannula 14 trocar 10 includes a trocar assembly 16 and a cannula assembly 18 the longitudinally extending or endoscopic portion of trocar assembly 16 which extends from trocar housing 20 is shielded from view in fig1 by cannula housing 21 and cannula 14 except for extended cutting tip 12 a circumferential abutment surface 15 is provided toward the distal end of cannula 14 referring now to fig2 and 3 pyramidal cutting tip 12 is rotatably mounted to obturator shaft 22 at swivel joint 24 a cylindrical channel 26 is formed in the proximal end of obturator shaft 22 a tension spring 28 see fig1 and 3 is.