The comparison in figure 3 indicates positive allometric growth in the brain of humans relative to chimps, and negative allometric growth in the jaw of humans relative to chimps. Thompson argued that changes in shape are global, rather than local. Something is controlling large regions of the skull, to change shape over time, rather than each small region changing independently. In figure 3, you'll notice that the human's mouth is similar to a young chimp's. We might then say that the growth of the mouth is arrested or retarded in the human, such that the human is locked in the fetal or young condition of its ancestor.
Humans are then quite like fetal apes.
Here we see paeodomorphosis, again. The adult human has the form of it's juvenile ancestor.