This same facial expression, which is a very striking one, exists in all races.
When children are still too young to contract the frontal muscle completely, they show surprise by a gaping mouth, and a puckering of the entire forehead, in place of the transverse furrows.
Expression of Thought.—In addition to the expressions of the emotions, the authorities describe those due to thought, and give special consideration to the expression of external or sensory attention, and internal attention (reflection, meditation). The young child is capable of intense sensorial attention, which is manifested especially in visual attention.
I have been able to make many observations in the "Children's Houses," where children two or three years old take part in games that demand attention, comparison, and the exercise of reason, without tiring their minds or encountering any great difficulty. These children wrinkle their foreheads and hold their mouths slightly open.
This is the expression also noted by Darwin, and the one which notoriously produces those vertical lines in the middle of the forehead, known as the lines of thought.
When these children are obliged to make an effort of thought or when they are for any reason troubled and anxious, slight contractions pass across their foreheads, like a continuous succession of broken shadows (Darwin).[45]
It should be noted that in any case a contraction of the eyebrows during intellectual work denotes effort, a difficulty to be overcome. Pure thought, by itself alone, produces no such contractions.
The contemplative man, absorbed in profound meditation, shows a face overspread with serenity, due to muscular repose; the gaze is fixed upon the void, and the head, as though no longer sustained by the relaxed muscles, is inclined forward.
If his eyes retain steadfastly the same original direction, even after the body has dropped forward, they give the impression of being turned on high. Such is the expression of the man sunk in profound thought, so long as his thought follows an uninterrupted course.