Abstract: The presenting unit (1) comprises a bottom wall (2), two lateral walls (3), a tool-carrying tray (4) placed on the bottom wall between the lateral walls, and a cover (5), the latter and the tray being detachably freely articulated to and hooked on a transverse pivot pin (6) carried by the lateral walls (3). The tray comprises a series of transverse corrugations defining alternating and parallel planes (13,14) inclined relative to the bottom wall. In one of the planes (14) are placed pellets (15) for retaining tools (17 . . . 20). Each plane (14) corresponds to a given type of tool. The cover (5) with its bottom wall (2) and lateral walls (3) and the tray (4) can be easily separated after raising the cover. The corrugations of appropriate inclination place the successive rows of tools (17 . . . 20) in a position in which they are easily taken hold of by the surgeon.