V
Their reasons why changes in the psychical state are reflected are numerous with such facility by the muscles of the face. Besides that of proximity to the nerve-centres propounded by Spencer and Darwin, there is the anatomical fact that the facial muscles have, for the most part, no antagonists. We know that in the hand, for instance, a slight contraction of the muscles which serve to open the hand and extend the fingers, is opposed by the action of the flexors which bend and contract the fingers. In the face the majority of the muscles can act freely, hence a slight nervous shock produces effects far more intense than in the other muscles of the body, in which the slight contraction of muscles acting in a contrary sense must always be overcome.
The muscles of the face are also more delicate, and have less volume than those of other parts of the body. Now the volume of the muscles exercises considerable influence on the greater or lesser facility with which they contract. A convincing proof is offered by the heart, in which, when life ceases, there is an almost immediate stoppage of the action of the ventricles, which form a thick, firm muscle, while the auricles, forming a fine muscle, continue to move for hours after all other parts are rigid in death.
Another anatomical fact of the greatest importance, brought into prominence by Meynart, is to be found in the origin of the facial nerve within the brain. All other nerves have a very intricate course, and are connected with other cells, and other nerve-filaments, which constitute the cerebral convolutions; the facial nerve only receives commands directly from the central parts of the brain and transmits them by the shortest route to the periphery. If I may allow myself to make use of a comparison, I should say that the facial nerve is like a telegraph wire, which transmits the messages directly to their destination, while with the other nerves the messages are sent successively from one station to another, consequently they pass less rapidly from the brain to their destination in the muscles.
The investigation of that part of the brain whence are issued the commands causing the contraction of the muscles, the accurate, microscopic examination of the cells which, by their activity in the deep parts of the brain, produce the expression of the physiognomy, is a new and important study.
An American anatomist, Mr. Edward Spitzka,[25] discovered that the facial nerve originates in two masses of nerve-cells, called, in anatomical language, nuclei.
There is a lower nucleus, the cells of which preside over the respiratory movements and the expression of the emotions, and an upper nucleus directing the orbicular muscle of the eye. While the latter presents very few variations when studied in different animals of the zoological series, the lower nucleus of the facial nerve, on the other hand, varies considerably, according to the development of the other muscles of the face.
In reptiles, for instance, the nucleus of the facial nerve which goes to the eye is well developed, while the lower nucleus is in a retrograde condition. In birds, which, like reptiles, have no muscles giving expression to the face, this mass of cells forming the lower nucleus is entirely lacking. In the elephant, on the other hand, the lower nucleus is well developed, because the nose is a complex organ requiring a special group of nerve-cells and nerves in order to act.
Spitzka’s anatomical researches having shown that the lower nucleus of the facial nerve reaches its maximum development in the monkey and in man, we must regard it as very probable that the nerve-cells which we see at this point in the brain, at the lower origin of the facial nerve, are really those which produce the expression of the physiognomy.
As I write this, I have before me a very thin section of the brain, showing the nucleus of the facial nerve as it appears in man. It is a gray spot, as large as the head of a small pin, slightly spindle-shaped, and having a volume of about two cubic millimetres. If we look at it under the microscope we see nothing but an accumulation of cells, about the five-hundredths of a millimetre in diameter, and with delicate branches intertwining with each other. In vain the eye tries to find a path through this intricate network of filaments and cells; imagination loses itself as in a labyrinth, and we remain humbled and almost frightened at the thought that we are contemplating the corpse of the noblest part of the brain. The activity of these cells has roused the most powerful emotions of our life: our knowledge of men, our sympathy, indifference, suspicion were provoked by the movements which they gave to the faces of those we have known; friendship, affection, and the most holy joys of life brightened our countenance with a smile which came from these cells; they, again, diffused the shadow of sadness, pain, and tears—and all this drew life from a part of the brain so minute that by a mere touch we could unconsciously crush it.