An open end bladder 1, in which the center of curvature of a curved portion which is the joint of the corner and the first oblique portion is located inside said bladder; the center of curvature of a curved portion which is the joint of said first oblique portion and the second oblique portion is located outside said bladder; and the center of curvature of {HEAD ~ the convex portion} curved and extending outward from {TAIL ~ the second oblique portions} and constituting the maximum diameter portion of said bladder is located inside said bladder 
An open end bladder 1 , in which the center of curvature of a curved portion which is the joint of the corner and the first oblique portion is located inside said bladder ; the center of curvature of a curved portion which is the joint of said first oblique portion and the second oblique portion is located outside said bladder ; and the center of curvature of { HEAD ~ the convex portion } curved and extending outward from { TAIL ~ the second oblique portions } and constituting the maximum diameter portion of said bladder is located inside said bladder
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