The oblong frame, with a semicircle on every corner and angular projections between them, divides the picture into three parts and Lorenzo Monaco made good use of the possibilities offered by the unusual shape of the frame. He placed the Virgin and her Child-isolated from the other figures-into the central, widest part.
The Virgin is riding the ass side-saddle, as though she were sitting on a throne, and she is turned towards us. To indicate the direction of her course, her body is a little bent backwards.
The oblique line of her body suggests a straight line between the upper point of the frame and the bottom inward angle on the right, and this diagonal axis is further stressed by the ass's foreleg, stepping forwards, which, continuing the same line, eventually ends in the semicircle. A similar connection between the composition and the frame can be observed in the hindmost leg of the ass and the bottom left semicircle.
The oblique line of the leg is a reflected image of the axis which was mentioned previously. The horizontal line of the animal's body links the figures of the Virgin and Joseph, and, at the same time, it separates the Holy Family from the women accompanying them. The palm branches in the hands of the woman in a green cloak, and the drapery falling downwards from her arm, practically creates a line between the top and the bottom angular indentations of the frame.
According to some apocryphal gospels the fleeing Holy Family was nourished by the fruits of a palm-tree bending towards them. The background, too, separates the left-hand side of the picture from the rest: the escorts proceed among bare, grey rocks, while the Holy Family move through woods: the foliage magically illuminates the semi-darkness.
