a frontal portion closed by transverse flaps that surround the front foot area the flaps are equipped with instep tongues that extend in the longitudinal direction of the boot these tongues are each connected by a sliding connecting element to the contiguous flank of the rear portion of shell base the connecting element guarantees the constant maintenance of the tongue with respect to the contiguous flank while still allowing substantial freedom of clearance from the instep zone application_number US 94254397 A description fig1 schematically illustrates a ski boot constituted of a shell base 1 equipped with a sole 8 and an upper portion 2 the upper portion 2 having tightening elements thereon as seen in fig1 the upper portion being represented in dotted and dashed lines in order to further highlight the specific structure of the shell base 1 in its zone corresponding to the instep 3 zone in this type of boot the shell base 1 has a rear portion 4 that encircles the ankle up to the vicinity of the instep 3 zone and a frontal portion 5 split longitudinally that encircles the front of the foot the latter is closed by transverse flaps 6 7 as can be seen clearly from the drawings of fig2 and 3 whereas the rear portion 4 has the shape.