The muscles of the head with few exceptions occupy the anterior region of the head and more particularly the face. They are divided into two very distinct classes—1st, the muscles which serve for mastication and move the lower jaw; and 2nd, the muscles which, under the influence of emotion, modify the traits of the countenance and serve for the expression of the emotions. We call these the muscles of expression.

The muscles of mastication present the general arrangement that we have already met with in the various muscles of the trunk and limbs. They are attached to the bones, and they have fleshy bellies, more or less thick, which swell up in contraction, and are marked by prominences, just as the contraction of the biceps is shown by the prominence it produces on the anterior surface of the arm. The muscles of expression, on the contrary, present a different type. These are muscles of the skin, which move the skin and not the parts of the skeleton; therefore their fleshy parts are in general very slender, and their contraction is not marked by any local swelling corresponding to the fleshy body, but only by change in place and form of the folds and membranous structures of the face (eyelids, lips, etc.). We will first study the muscles of mastication.

Muscles of mastication.—The muscles which move the lower jaw are inserted into the ramus and angle of the bone. Those on the inner side of the jaw are the deeply placed pterygoid muscles (so called because they arise from the pterygoid process of the sphenoid bone). We need not dwell on these muscles here, for they are deeply hidden in the zygomatic fossa of the head, and are not visible in any part on the surface. Those on the outer side are inserted either into the ramus and angle of the bone (masseter muscle) or into the coronoid process (temporal muscle).

The masseter muscle is a quadrilateral fleshy mass (12, Fig. 88) of which the upper attachment arises from the zygomatic arch (Fig. 56), and the lower attachment is inserted into the ramus and angle of the jaw. The anterior border of this muscle is thick, and in thin subjects forms a prominence, in front of which the cheeks are sunk so as to produce a more or less marked depression. In contraction the masseter raises the lower jaw and brings it into contact with the upper, against which it presses strongly. It would be superfluous to dwell here on the part this muscle plays in mastication. It is more important to remark that during violent emotions, or even when we accomplish a powerful effort, we involuntarily clench the jaws. Contracting the masseter, therefore, in anger, menace, and in the strong expression which we characterise commonly by saying that the subject grinds his teeth, we see the masseter shown in the form of a quadrilateral prominence on the side of the face. Therefore the accentuation of the form of the masseter contributes to give to the physiognomy an energetic expression, and generally that of brute force.

The temporal muscle (4, Fig. 88) occupies the entire extent of the temporal fossa of the skull (Fig. 56); it arises from the bones that form that fossa and from an aponeurosis which, arising from the borders of the fossa, is attached to the upper border of the zygomatic arch, so as to form a species of cover (temporal fascia) to the fossa in question. From these multiple points of origin the fleshy fibres converge below and form a strong tendon which embraces the coronoid process of the inferior maxillary bone (25, Fig. 56), into which it is inserted. This muscle raises the lower jaw, but as it is shut up, so to speak, in a close space (temporal fossa and aponeurotic cover) it does not show during its contraction a remarkable prominence in the temporal region; nevertheless, in a person performing the movements of mastication we see the skin of the temple, above the zygomatic arch, slightly raised in a series of rhythmical movements; these movements alone show externally the contractions of this muscle during mastication.

Muscles of expression.—From what we have already said respecting the peculiar arrangement of these muscles of the skin, it is easy to understand that their study must be undertaken in a totally different manner from that of the muscles of the skeleton. We do not seek so much to define the form of the fleshy masses as to trace the direction along which each muscle exercises traction on the skin. Given the bony or cutaneous attachments of the muscle, we must observe the direction in which it acts, and so define the form of the folds or wrinkles which it causes on the skin, and ascertain what facial expression is acquired by these changes. Before we enter into these details, it is necessary to glance rapidly at the history of this particular question of human physiognomy, and then to consider the method by which its study should be undertaken.

First we must remark that we study here, with regard to the muscles of the face, physiognomy in a state of action—namely, the characters that affect the features at a given moment, under the influence of a passionate movement which causes (it may be) the involuntary contraction of one of the numerous muscles of the skin. Indeed, we may almost assert that the muscles of the face might be given names associated with mental states—attention, pain, menace, laughter, sorrow, contempt, disgust, &c. But we cannot pretend to study physiognomy in a state of repose, or to learn by the normal and permanent accentuation of certain of these traits the character of the subject and the passions that most frequently disturb him.

Doubtless, these two studies have numerous points in common; it is easy to admit that, in a subject who is governed by one prevailing or overpowering emotion, such as suspicion, grief, or pain, the permanent or frequently repeated contraction of the muscles which correspond to these emotions can definitely mould the character of the face, so as to leave imprinted on it in a permanent form the sentiments that govern the mind.

But this analysis of the character of a subject is a very delicate study, always very uncertain, and admitting of philosophical developments which would carry us far away from the domain of anatomy. On the other hand, the determination of characteristic expressions impressed upon the face by the contraction of this or that muscle has, from the researches of Duchenne (of Boulogne), become a study which presents all the precision and certainty that we can claim from facts strictly deduced from anatomy.

Before the researches of Duchenne, the majority of books written on expression dealt almost entirely with physiognomy, or the means of recognising the character by the study of the habitual state of the traits of the countenance. We shall, in the first place, mention the works of Le Brun, Camper, Lavater, C. Bell, Humbert de Superville, and Sue, and then we shall refer to the investigations of Duchenne and Darwin.

Long ago, in the drawings of Leonardo da Vinci, we find some valuable indications of the state of the face and neck in the expression of the emotions. This great master, for example, clearly perceived the part that the platysma muscle of the neck takes in the expression of violent passions, and portrayed the transverse folds which then mark it beneath the chin. Le Brun, however, was the first to arrange studies of this character into a doctrinal series. The publications in which his views on this subject have been preserved are numerous.[7] The artist will find there a number of interesting observations, curious comparisons, and ingenious explanations. Le Brun occupied himself principally with the resemblance of certain types of human physiognomies to the heads of animals; in short, he studied physiognomy in relation to character.

Camper, whose works we have already quoted respecting the facial angle (page 181), was an anatomist and an artist. He analysed the action of the facial muscles, and it was he who first laid down this general rule—viz. that the contraction of each muscle of the face produced in the skin one or more folds, of which the direction is always at right angles to that of the muscle, a precept that we shall find to be true with regard to almost every muscle of the face, and especially for the frontalis, the great zygomatic, &c. Besides the exact observations that the artist will meet in the works of Camper, he will find in addition an interesting historical account of the question.

An English anatomist, Sir Charles Bell, celebrated for his studies of the nervous system, also analysed the expressions of the face.[8] But though his work affords picturesque descriptions and admirable illustrations, it is more interesting to the anatomist than the artist.

The title of the work of Lavater (The Art of Knowing Man by his Countenance)[9] indicates the object sought by the author. We find in this work good illustrations, and curious observations especially applicable to the study of physiognomy, but frequently without order, without method, and accompanied by dissertations on whimsical subjects, such as the chapters devoted to imaginations and envies, to warts and beards, and to lines of animality, &c.

In order to have an idea of the manner in which, at this epoch, authors attempted the study of physiognomy, making this delicate analysis a pure affair of sentiment, it is sufficient to mention the work of Sue (Physionomie des Corps Vivants, considéré depuis l’Homme jusqu’à la Plante. Paris, 1797.) In the middle of a long affected treatise on physiognomy and its relation to the passions, this, for example, is how he expresses himself concerning the mouth:—“A mouth delicate and pure is perhaps one of the best recommendations. The beauty of the portal proclaims the dignity of that which passes through. Here also is the voice, the interpreter of the heart and mind, the expression of truth, friendship, and the most tender sentiments.” With regard to the incessant comparison of human physiognomy with that of animals, the author stops at nothing in this singular course, and speaks dogmatically on the physiognomy of fishes, serpents, grasshoppers, and intestinal worms (!), as well as that of man. “Many fishes,” said he, “are wanting in that which gives a character of amenity, kindness, and tenderness.” “The intestinal worms have a very decided physiognomy ... the character of their physiognomy inspires in man sorrow and awe.”

Amidst the works of a more serious, though still empirical character, we must mention in particular one which, although dealing with the countenance only in a secondary degree, yet presents several valuable observations on this subject. We have endeavoured to utilise these investigations in the diagrammatic representation of the action of the muscles of the face. We speak of the treatise of Humbert de Superville (Des Signes Inconscients de l’Art, 1827). The author gives three drawings of the human face, in which the lines represent the eyes, the lower boundary of the nose, and the lips. In one of these drawings (Fig. 90) the lines are all horizontal, in the second (Fig. 91) they are all inclined downwards and outwards (from the median line), and in the third (Fig. 92) they are all inclined upwards and outwards. The author remarks that the first figure (with the lines horizontal) produces an impression of calmness, greatness, and constancy; and he adds that in the same way in nature and architecture horizontal lines give rise to the idea of calmness, stability, and grandeur: the cedar, with its horizontal branches, is of all the trees the one that realises this impression in the highest degree. On the contrary, the second figure (with the lines directed obliquely downwards) gives an impression of sadness, pain, and grief; and the author does not fail to compare the direction of the features of such a countenance with the direction of the architectural lines in tombs and funeral monuments, and that of the branches of the trees which everywhere are planted in preference to others in cemeteries, and whose branches always hang obliquely. Lastly, the third figure (with the lines obliquely upwards) gives rise to the impression of gaiety, laughter, levity, inconstancy; and, to continue the preceding comparison, everyone must acknowledge that Chinese architecture, with its lines oblique and diverging upwards and outwards, can never—at least, in the eyes of a European—produce an impression of grandeur and majesty.

These figures, and the remarks that de Superville makes afterwards, but which we have not emphasised here, are strikingly exact, when we consider the features in the state of movement or in a momentary expression of emotion. All the muscles which take part in the expression of pain, sadness, and contempt help to incline the features obliquely downwards and outwards, some by acting on the outline of the eyes, others on that of the mouth, &c. On the contrary, the muscles of laughter, raising its angles, draw the mouth obliquely upwards and outwards, and—for certain reasons that we will analyse further on—seems to give a similar direction to the outline of the eyes. In a word, features, starting from the state of repose, represented by the first figure of Humbert de Superville (Fig. 90), oscillate in two opposite directions, either ascending, to express the scale of gaiety and laughter (in which the features are oblique upwards and outwards, Fig. 92), or descending—sadness, pain, and tears (in which the features are oblique downwards and outwards, Fig. 91). The exactness of the drawings furnished by Humbert de Superville for the general expression of the physiognomy induces us to try, by similar drawings, to represent the action of each muscle separately. Knowing the action of a muscle, and knowing from the photographs of Duchenne the direction that it imparts to a certain feature of the face, either to the line of the eyebrows, the opening of the eyelids, the nostrils, or the lips, we have indicated by a simple stroke or line these changes, either in direction or in the form of one of those lines, and have obtained theoretical figures sufficiently expressive to characterise the emotion geometrically, so to speak, in the manifestation of which this or that muscle is affected. Such are the Figures 96, 98, 100, 102, 103, 104, 106 (page 317 and following), by means of which we will attempt to explain the action of each muscle of expression. We may say that these drawings, without any pretension, are, so to speak, the primer of the language of physiognomy.

We now arrive at the history of the work of Duchenne, to which we owe all that follows. While all his predecessors had been taken up with observation, Duchenne introduced the experimental method into the study of physiognomy. His process, simple in conception, was very delicate in application. His method was to cause the contraction of each muscle singly, and that the expression that resulted might be appreciated not only at the moment of the experiment, but again at any time, and submitted to the judgment of all, he photographed the subject at the moment when the muscle was contracted. This last operation was easily accomplished, but the excitation of a single muscle was a more delicate operation. Everyone knows that by electricity, in placing the two electric needles (the two poles of the current) on the course of a muscle, we can cause the contraction of the muscle beneath the skin. But no subject would lend himself to this experiment. At first he tried on the dead body of an executed criminal a short time after death; but the muscles of the face lose their excitability two hours after death, and then it is only by actual exposure of the muscle and direct stimulation that we can obtain contraction by the application of electricity. On the other hand, if we attempt it on any living subject, we can, it is true, cause a muscle to contract by applying electricity over its site; but the electric current, traversing the skin to reach the muscle, at the same time that it excites the motor nerves of the muscle, excites also the sensory nerves of the skin and produces acute pain. From this fact we see that we produce on the face of the subject, not a simple and characteristic expression, but a true grimace, or an irregular contraction of all the muscles under the influence of the pain.

Duchenne had the good fortune to be able to experiment on a subject in whom a particular infirmity rendered impossible the last inconvenience we have noted. This was an old pensioner of the hospital who had anæsthesia of the face (ἀνα, absence of; αἴσθησις, sensibility), in whom the skin of the countenance was insensible to the most painful excitation; electricity could be applied to the skin without producing any painful reaction, and yet excited the muscles beneath, which had perfectly preserved their contractility, and performed their functions as in a normal subject. He could, therefore, cause this or that muscle to contract alone, and could excite, for example, the action of the great zygomatic, giving to the face the expression of laughter, without the subject having any idea of what his physiognomy reflected; his face, by the action of the electricity, was laughing, while his thoughts might be indifferent or fixed on sad recollections; on the other hand, for example, by the contraction of the superciliary muscle, his countenance might express the most acute pain, while his thoughts might be quite indifferent or borne away by gay and pleasant ideas. In a word, Duchenne was able to realise, under the most precise conditions of experiment, an exact study of the uses of the muscles of expression.

The work in which Duchenne has given the result of his labours is remarkable particularly for the magnificent atlas of photographs that accompany it, and which have been obtained by the above process. From these photographs have been reproduced as exactly as possible the several figures that accompany the descriptions which follow (Figs. 95, 97, 99, 101, page 316 and following). We cannot enter here into a complete statement of the results obtained by Duchenne, but we will seek at least to show the serious and scientific value of these studies, and to inspire the student to refer to the original work.

These studies have for the artist this important result—namely, to prove to him that frequently the contraction of a single muscle is sufficient to express an emotion, and that it is not necessary to change all the features in order to give to the face the stamp of pain, attention, menace, contempt, disgust, &c., each of these sentiments being expressed by a slight modification, either of the eye alone, or of the lip alone. Each expression has, so to speak, its own exact, precise, and separate mark, produced by a single local modification; but this local modification seems to be reflected throughout the physiognomy, and therefore, from unaided observation, artists had for a long time believed that, for example, attention and pain were shown by the combined action of a number of facial muscles. Now experiment proves that pain may be expressed solely by a muscle which raises and wrinkles the brows, and on a face (Fig. 99) where this muscle alone is contracted (superciliary muscle, page 320) the expression of pain is complete. We naturally believe that the mouth also takes part in it, but if we cover the upper part of the countenance, we perceive that the lower part of the face is in a state of complete repose.

To bring to a close this history, which is not the least interesting part of the subject, we must say that the labours of Duchenne were not at first received with great favour in France. Physiologists as well as artists showed a certain distrust of a work which pretended to give precise rules and scientific laws to a subject about which it had been the custom to make fanciful and sentimental comparisons. Few persons understood the nature of the reason which forced Duchenne to choose as a subject for these experiments a poor man with a physiognomy almost imbecile in repose, and they did not consider that if this face was old, wrinkled, thin, and vulgar, there was the greater reason to be struck with the precision with which the electric excitation enabled the most opposite and characteristic expressions to be taken.

As has been too often the fate of scientific discoveries, the work of Duchenne was neglected in France, and was not appreciated until it had been adopted by a foreign country. It was Darwin who made the results of the French physiologist the basis of his own interesting studies.

It is not necessary to recall the extent and repute of the works of Darwin on The Origin of Species, on the Evolution of Animals and Plants, and on The Descent of Man. What this great naturalist has done for the general morphology of plants and animals he sought to do for the subject of physiognomy. Seeking in the logical chain of natural facts the cause of all biological phenomena, he endeavoured to discover by the attentive study of the movements of expression, and through their origin and development, a series of new arguments in favour of the theory of evolution. In a word, Darwin, by invoking the association of certain useful movements, and comparing the functions with the expressions with which they are associated, sought to explain why one muscle in particular rather than another is affected by the expression of this or that emotion. We cannot here enter further into the analysis of this philosophical work. It is sufficient to remark (having commended the perusal of it as most interesting to the artist[10]) that before we explain anything it is necessary that it should be firmly established. Therefore the explanation of the part that each muscle takes in the expression must be impossible until the fact of the action and the expression associated with the movement of the muscle has been scientifically demonstrated. The philosophical work of Darwin could not have been undertaken if it had not been preceded by the experimental work of Duchenne.

Summarising Darwin’s argument, his thesis may be stated somewhat as follows: that every expression or bodily manifestation of emotion has a physical basis, and an origin in some useful exercise of the particular muscles concerned; that such an action becomes habitual in the individual, and is transmitted from father to son, and from generation to generation; and that the actual physical cause is transferred to a mental condition, so that an action like knitting the brows—primitively for the purpose of actually clearer vision—becomes indicative of a mental state in which the emotion is expressed of a desire for a clearer mental vision, as when a man is engaged in any intellectual problem.

Darwin further enunciated the important principle of Antithesis: which means the employment of exactly the opposite expression (it may be by the relaxation of muscles, or by the contraction of antagonistic muscles), to indicate an opposite or antagonistic attitude of mind. Thus joy is expressed by the contraction of a definite series of facial muscles; grief or dejection is expressed by the relaxation of these and the contraction of opposing muscles. The healthy, alert man holds his head erect; the depressed or miserable has a drooping gait.

A third principle enunciated by Darwin as employed in producing the expression of emotion is the direct action of the nervous system, to a large extent independent of the will, and served mainly through the sympathetic nervous system, such as blushing, trembling, perspiration, &c.

It is important, as Darwin points out, to bear in mind that emotion is expressed not only by facial expression, but by many other agencies as well; by the emission of sounds, by the voice in some cases, by the rattling of the tail quills in the case of the porcupine, &c.; by the inflation of the body, as in the hen who raises up all her feathers in maternal anger, or the dog whose hair stands on end; by gestures, rubbing, licking, caresses, kisses; or by the attitude and movements of the body, head, or limbs.

In his book each emotion and its corresponding expression is carefully analysed, and the physical cause and the particular muscles engaged are pointed out. Thus Darwin says, “Weeping is the result of some such chain as follows: Children wanting food or suffering in any way, cry out loudly as a call to their parents for aid, like the young of most animals. Prolonged screaming leads to the gorging of the blood vessels of the eyes; and this causes first consciously and then habitually the contraction of the muscles round the eyes in order to protect them.” The mouth at the same time is opened widely to allow of a more vigorous scream. The overflow of tears is a consequence of the closure of the eyes.

Again, in regard to the facial expression in laughter, Darwin suggests that as the primitive cause of laughter may have been a practical joke—or, as De Rochefoucauld put it, there is something pleasing in the misfortunes of one’s friends—the expression may be associated with the retraction of the angles of the mouth, and the exposure of the canine teeth, in preparation for self-defence if the victim of the joke should retaliate.

The expression of disdain or disgust in the same way is associated with the contraction of muscles of the eye, nose, and mouth, primitively from purely physical causes, which have become connected with a mental attitude. The head is turned aside, and the eye is half closed to shut out an unpleasant sight; the nostril is raised at the sensation of a disagreeable smell, and the lips are curled in disgust at a nasty taste.

There is not space in which to dwell further on these deeply interesting questions, for a study of which the reader is referred to Darwin’s masterly treatise on the subject.

The figures which illustrate the work of Darwin are in a great measure only reproductions of the photographs published by Duchenne about ten years previously. However, as we have already mentioned, attention has been recalled in France to the works of Duchenne, a more favourable judgment has been passed, and justice has been rendered to him who had opened the way to the experimental study of physiognomy. In 1874 the French began to devote, in the course of anatomy in the School of Fine Arts, several lectures to the account of what we must call the primer or grammar of the expression of physiognomy. Happy in seeing his works included in this classical course of instruction, Duchenne, whom death carried off a few years later, gave to the School of Fine Arts the complete series of large original photographs from which these publications are reduced, and this beautiful collection is to-day one of the most valuable in the French museum of anatomy (Muséum Hugnier).

Although this account may appear long, it is nevertheless very incomplete, being given only with a particular object—that of comparing the works of Duchenne with those preceding him. Those of Duchenne will be made the basis of the studies which follow. We will finish by noting, as interesting and instructive, the works that treat in a more general manner of expression and physiognomy, such as those of Lemoine, Gratiolet, and Piderit.[11]