These figures are renderings of what is called the cortical homunculi. The size of their features represent the relative proportions of the parts of the human brain responsible for motor and somatosensory function. So the features that are most exaggerated have the largest correlate representations in the brain. Take the hands, for example. They are the most dexterous parts of the human body, with large representation in the brain. We sense and manipulate a great deal through them. Therefore they are extremely exaggerated in sensory and motor homunculus.

The smartphone homunculus is how we imagine we, and probably you, look like today. He spends his days looking at a 2-dimensional glass display, probably between 4-inches and 14-inches across. That's why he only needs that one eye. No need for stereo vision. He interacts with this display using his index finger (and occasionally one or two other fingers, when a snazzy multi-touch app supports it), and sometimes his tiny ears take auditory cues ("turn left", "turn right") from his navigation app.

Gershon and Nan