Final answer:
Orthogonals are diagonal lines in linear perspective that converge at a vanishing point, creating the illusion of depth in drawings and paintings such as Masaccio's or Perugino's works. In the Mona Lisa, these lines guide the eye towards the horizon, contributing to the painting's spatial coherence.
Step-by-step explanation:
The subject in question pertains to matching a foundation drawing to an orthographic drawing by examining linear perspective, specifically focusing on orthogonals. In the context of Masaccio's painting referenced in the question, orthogonals are the diagonal lines that suggest depth by converging toward a vanishing point, in this case, below the base of the cross as viewed from a low angle. Similarly, by examining Perugino's painting, one can overlay lines to see how orthogonals lead to a vanishing point and create an illusion of space and form.
When inquiring about Leonardo da Vinci's iconic Mona Lisa, observation of the painting's linear perspective will reveal that the implied orthogonals in the background landscape guide the viewer's eye towards the horizon, suggesting depth and spatial coherence. However, the elusive quality of the Mona Lisa's smile might be what draws the most attention, rather than the technical use of perspective in the artwork.