the invention relates to a manifold , of the type comprising a substantially flat plate with holes to accept tubes of a heat exchanger , and turned - up lateral edges extending at an angle to said plate and connected thereto by at least one curved portion in which ribs are formed , the ribs each having a convexity extending substantially in the direction of extension of the lateral edges . the plate comprises at least one additional rib between at least some of said holes , which ribs each have a convexity extending substantially in the opposite direction to the direction in which the lateral edges extend .