"To this end, the inner sidewall 22 includes a resiliently flexible, or distensible, depending end portion 32, which is formed in such manner as to define an interiorly disposed peripheral sealing section which, as will be subsequently described, is adapted to contact the dispensing end 41 of the container 40 in frictionally slidable, fluid-tight, sealing relationship when the closure 20 is threada" . . . .