A system for mounting a side glazed unit of a means of transport, in particular a train glazed unit, in a peripheral opening, said glazed unit being a multiple, fixed, glazed unit having an outer face that faces an external space and an inner face that faces an internal space, said outer face of the glazed unit being continuous in appearance with an outer flank of said opening over its entire periphery, said glazed unit including: - an outer glass pane having an outer face which faces the outer space, a peripheral edge and an intermediate face opposite the outer face, said outer glass pane preferably being laminated and then comprising at least one outer glass sheet, an inner glass sheet, as well as a plastic sheet located between said outer glass sheet and said inner glass sheet, each sheet (3, 4, 5) of said outer glass pane having a peripheral edge (30, 40, 50), - an inner glass pane having an inner face that faces the inner space, an intermediate face opposite the inner face, as well as a peripheral edge, - an internal structure which is located at the internal periphery of said outer glass pane and at the internal periphery of said inner glass pane while being at least in part further towards the center of the glazed unit than the peripheral edge (20, 60) respectively of said outer glass pane and of said inner glass pane, and which holds together these two glass panes (2, 6) in such a way that the glazed unit provides a separation between said external space and said internal space with a glazed unit cavity located between said glass panes (2, 6), said internal structure including a connecting cavity having a centripetal bottom and a centrifugal opening, said opening including a lock which is mounted in said opening and is located more centrifugally than the edge of said inner glass pane, said lock having a lateral wing extending into said connecting cavity and opposite an edge of said intermediate face of the inner glass pane by 90° rotation of said lateral wing, an outer seal, preferably hollow, being located in a mounting space between on the one hand said outer flank and on the other hand the edge of said outer glass pane or on the other hand the edge of said outer glass sheet, said outer seal having an inner face, characterized in that, said lock includes at least one protrusion, and preferably includes a first protrusion and a second protrusion, extending towards the external space, said outer seal comprising a groove extending from said inner face toward the external space, - said protrusion, and preferably said protrusions (10a, 10b), being intended to be housed in said groove when said lateral wing is arranged in said connecting cavity, the lock being in the closed position, and - said protrusion, and preferably said protrusions (10a, 10b), being intended to bear on said inner face of said outer seal when the lock is in another position than the closed position. - an outer glass pane having an outer face which faces the outer space, a peripheral edge and an intermediate face opposite the outer face, said outer glass pane preferably being laminated and then comprising at least one outer glass sheet, an inner glass sheet, as well as a plastic sheet located between said outer glass sheet and said inner glass sheet, each sheet (3, 4, 5) of said outer glass pane having a peripheral edge (30, 40, 50), - an inner glass pane having an inner face that faces the inner space, an intermediate face opposite the inner face, as well as a peripheral edge, - an internal structure which is located at the internal periphery of said outer glass pane and at the internal periphery of said inner glass pane while being at least in part further towards the center of the glazed unit than the peripheral edge (20, 60) respectively of said outer glass pane and of said inner glass pane, and which holds together these two glass panes (2, 6) in such a way that the glazed unit provides a separation between said external space and said internal space with a glazed unit cavity located between said glass panes (2, 6), said internal structure including a connecting cavity having a centripetal bottom and a centrifugal opening, said opening including a lock which is mounted in said opening and is located more centrifugally than the edge of said inner glass pane, said lock having a lateral wing extending into said connecting cavity and opposite an edge of said intermediate face of the inner glass pane by 90° rotation of said lateral wing, an outer seal, preferably hollow, being located in a mounting space between on the one hand said outer flank and on the other hand the edge of said outer glass pane or on the other hand the edge of said outer glass sheet, said outer seal having an inner face, characterized in that, said lock includes at least one protrusion, and preferably includes a first protrusion and a second protrusion, extending towards the external space, said outer seal comprising a groove extending from said inner face toward the external space, - said protrusion, and preferably said protrusions (10a, 10b), being intended to be housed in said groove when said lateral wing is arranged in said connecting cavity, the lock being in the closed position, and - said protrusion, and preferably said protrusions (10a, 10b), being intended to bear on said inner face of said outer seal when the lock is in another position than the closed position.