in which the bolt 17 is accommodated completely within the body 14 and does not project into the slot 15 as illustrated in fig4 the bolt 17 comprises a stud 18 projecting perpendicularly to the axis a and to the slot 15 through an oblong aperture 19 formed in the body 14 along the axis a so as to allow the displacement of the bolt 17 according to one embodiment the bolt comprises two studs 18 radially opposed and extending on either side of the bolt 17 through corresponding apertures 19 furthermore the body 14 comprises an oblong orifice or groove 20 extending obliquely with respect to the slot 15 and to the oblong aperture 19 between a first end located in the vicinity of the slot 15 and of the oblong aperture 19 and a second end located in the vicinity of an axis of articulation 21 the function of which is described below the locking device 13 comprises furthermore a cam 22 of elongate shape comprising a first and a second end the cam is mounted pivotably in the region of its first end on the body 14 of the locking system 13 about the axis 21 the cam 22 comprises moreover an oblong hole 23 in the region of its second end the stud 18 of the bolt 17 projecting into the oblong hole 23 more specifically the oblong hole 23 extends along an axis substantially perpendicular to the axis a of displacement of the bolt 17 the cam 22 comprises moreover a track 24 formed by an oblong aperture in the general form.