form a circumferential skirt which in the closed position encloses the frame 1 and thus projects some distance down along the latter reckoned from its outside if the sash consists of wood it may however be more expedient to provide it with a separate jacket which forms the circumferential skirt and in addition can carry or secure the window pane in the lateral frame elements 5 there are in the zone at the middle of the latter accommodated a pair of pins 9 each of which is rigidly connected to a link 10 which furthermore is pivotally connected to the sash 2 in the vicinity of the lower corners of the latter which are thereby during the opening and closing of the window forced to follow a circular arc around the common axis of the pins 9 the sash 2 is additionally guided in relation to the frame 1 by means of slide rails 11 which are placed along the sides 5 8 of the window and may be of a conventional type and are consequently not shown in detail each slide rail is here supposed to consist of at least three sections viz a lower section which is secured to the lateral frame element 5 and an upper section which by means of a pin 12 is hinged to the sash 2 near the top edge of the latter as well as at least one intermediate section which forms a telescopic connection between the two former sections it may.