A wide sheet of the facial musculature—the platysma myoides—extends into the subcutaneous tissue of the neck. Under normal circumstances this muscle acts on the mouth and jaw, drawing them downwards and backwards. When an effort is made with teeth clenched and all the muscles of the body straining, the action of the platysma is reversed ; its fixed point is in the face, and the muscle stretches and tightens the skin of the neck. The significance of this action is unknown. The platysma is the remains of a system of musculature which forms a complete sheet under the skin of the trunk of many mammals. It endows the skin with mobility. Every one knows how the horse can twitch the summer flies from its sides. In man and the anthropoid apes the muscles of the face and neck are all that remains of a great sheet, which in some animals is seen to be spread under the skin of the whole trunk.
The facial muscles of man are remarkable for their degree of differentiation and for their relatively small size. The great anthropoids have really the same muscles but have them somewhat differently arranged and somewhat less distinctly separated from one another. In the gibbon and monkeys of the old and new worlds the facial system becomes still simpler and at the same time more robust. It is a remarkable fact that the facial muscles of primates keep pace in their evolution with the brain ; as the convolutions increase in number and capacity, the muscles of the face become smaller and more finely differentiated. The study of anatomy therefore supports the experience of our every-day life that much can be learned of mental character and capacity from the muscles of the face. It is clear that they are evolved as the servants of the brain. The human brain, however, has the power of mastering and masking true feelings, and hence it is also true that a smiling face may mask a sad heart.
The story of the evolution of the muscles of the face is a very wonderful one. It has already been said that the whole of the facial system is supplied by the seventh cranial nerve. In fishes and lower vertebrates the seventh is the nerve of the second or hyoid branchial arch, supplying the muscles of that arch; in the human embryo the nerve lies within the hyoid arch. It is from this arch that the gill-cover and its muscles are developed in fishes. Now it is a remarkable thing that the muscles of the face should be supplied by the nerve of the gill-cover arch and still more remarkable that the muscles of the face should first appear in, and be produced from this arch. Arising over the side of the arch they spread out under the skin of the face and take up their final position round the eyes, nose, mouth and ear. All the links in the chain of evolution we do not yet know, but we can only explain the nerve supply and origin of the facial muscles by supposing that they have been modified somehow from the actively moving respiratory gill-cover of fishes. It is worthy of note that when we are winded we do bring the platysma of our necks actively into use during forced respirations.
The external ear also arises in connexion with the branchial system. The ear passage represents the upper end of the first cleft and the ear is developed round it from a series of outgrowths. The muscles which move it are derived from the same sheet as the muscles of expression. In man these muscles are small, often vestigial. Besides very minute muscles which are situated on the ear itself there are three muscles which act on it as a whole —one which can pull it upwards, another forwards and a third backwards. In a few individuals these muscles may actually move the ear at will but they cannot really be called muscles of expression in man. In the great anthropoids these muscles are as much reduced as in man; in the orang they are even more so, for in that animal the outer ear is of very small size and closely applied to the head. In monkeys the muscles are larger and the ear can be moved, but not with that flexibility which is characteristic of such animals as the dog and horse ; in which the ears are truly organs of expression as well as of hearing. When a monkey is angry it draws its ears backwards.
I am not aware of any one having studied the external ear as a clue to character, nor is there any fact which leads us to suppose such a study would be profitable. On the other hand it has been alleged that the ear may serve as an index to that type of man who is regarded as a" degenerate," an individual who is lacking in self-control and who is inclined to sacrifice the good of the community to selfish and evil passions. Certain features, such as abnormal crumpling up or infolding of the ear, and the absence of a lobule have been supposed to indicate such a tendency. The evidence on the whole is against the theory that an inferior nature is stamped by certain traits of the ear or any other part of the body, but an enquiry into this matter is attended with great difficulty owing to the extraordinary variability of the outer ear.
It is a remarkable fact that the outer ear of the great anthropoids and man are similar in type. In all of them the ear has lost its tip or point; only a remnant may be seen towards the upper part of the posterior border on the inturned margin of the ear. There is a distinct sexual difference; the ears of women are smaller and more folded than those of men and the lobule is usually larger. There is an age change ; after fifty the ear begins to enlarge. The ear also varies with race, one could tell a Bushman by his small ears, with the hinder margins curved over to form a wide welt. In other races the ears are large and project from the sides of the head, as is invariably the case in the chimpanzee. Indeed it is possible in every community to see some individuals who in type of ear recall the reduced form seen in the orang, some the large outstanding ear of the chimpanzee, and some the medium sized ears of the gorilla closely appressed to the head. The degeneration of the external ear in man and anthropoids is another result of the upright posture ; they turn their heads, in place of their ears, in the direction from which a sound appears to come.