Abstract: The lock is of the type comprising a pivotal fork member movable between an unlocking position towards which it is biased resiliently and a locking position. A detent means is carried by an arm of a pivotal first lever which has two arms and is movable between a retaining position and a releasing position relative to a projecting portion of said fork member and biased towards the releasing position by an unlocking force exerted on the fork member. A second lever is mounted to pivot between a first position, towards which it is returned resiliently and in which it locks an end of the second arm of the first lever when the first lever is in its retaining position, and a second position in which it releases said end and towards which it can be shifted.