Extra thin French/Swiss platinum lever dress watch Circa 1938

Platinum hunting cased keyless lever 
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An extremely fine, very rare and extra thin French/Swiss platinum hunting cased knife edged (montre couteau) keyless dress watch made by Cartier in Paris, circa 1938. The rhodium plated movement by European Watch & Clock Co Inc. with 19 jewels, a straight line lever escapement, cut bimetallic compensation balance adjusted to eight positions, blued steel flat balance spring and an index regulator. Matte silver dial with Roman hour numerals, an outer minute track and original blued steel Breguet hands. A polished case. Dial signed Cartier.
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Diameter: 49 mm
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Thickness: 4 mm
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Signed:
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The case is of unusual construction. The movement is housed in an adapter ring, of which the top portion forms the bezel. The thickness of the movement is only 2 mm.
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Couteau is the term used by Cartier in their manufacturing records to describe the type of ultra thin watches with knife edged cases, open faced or hunting cased models. These watches, with thicknesses of less than 4 mm for the open faced and less than 5 mm for the hunting cased version, are among the thinnest mechanical watches ever produced.
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For these thin watches from the first half of the 20th century, Cartier used movements from Edmund Jaeger (Jaeger-LeCoultre), who had just invented a movement only 2 mm thick. In the 1920s, Cartier and Jaeger formed a joint venture, the European Watch & Clock Co., whose signature can be found on many Cartier movements. Movements were further sourced from Vacheron & Constantin, who, from 1940, utilized a movement which was only 1.31 mm thick.