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Popular Science Monthly/Volume 4/March 1874/The Facial Angle

< Popular Science Monthly‎ | Volume 4‎ | March 1874

THE FACIAL ANGLE.
By RANSOM DEXTER, A. M., M. D.,

PROFESSOR OF ZOOLOGY AND PHYSIOLOGY IN THE UNIVERSITY OF CHICAGO.

THE methods of estimating the facial angle hitherto adopted by naturalists are all mere modifications of that proposed by Peter Camper, and consist in describing an angle with one line passing along the base of the skull, intersected by another which passes from the anterior portion of the upper jaw over the forehead.

Prof. Owen's definition is: "If a line be drawn from the occipital condyle along the floor of the nostrils, and be intersected by a second, touching the most prominent parts of the forehead and upper jaw, the intersected angle is called the facial angle" (vol. ii., p. 572, "Anatomy of Vertebrates").

The relation of the face is not to the base of the skull, or the plane from the floor of the nostrils to its articulation to the backbone, but to the axis of the body; for the face, in the lowest class of animals that have a backbone, the fish, is in line with the base of the skull, the axis of the body, and the dorsal surface of the animal; and in man, the highest class, the face is in line with the abdominal surface, and axis of the body. But the base of the skull does not keep in harmony, but varies irregularly. Then, there are numerous other elements than the bones at the base of the skull, that are factors in the aspect of the face, as, the modified development of other bones of the skull, peculiar development of bones of the face, and relation of the bones of the face that are not attached to the skull, but to other facial bones.

To make the subject more clearly comprehensible, it will be necessary to trace more in detail the development of the division of animals to be considered.

The subject of the facial angle has occupied the attention of philosophers from the earliest antiquity. Their theories, though vague, unsatisfactory, and uninteresting in themselves, yet tend conclusively to show that some patent general principle underlies the whole domain of the subject. Confined, as they were, to the narrow limits of the varieties of the human race, they would get only a part of the evidence that is so beautifully illustrated, when we include the whole sub-kingdom of animals to which we belong.

At the beginning of the present century, Cuvier, Von Baer, and others, discovered and established the great laws of evolution. The laws thus elucidated were: 1. That the entire animal kingdom originates from an ancestral egg; eggs, too, though differing in physical appearance, that are quite similar in structure. 2. That every animal, in its evolution, had to pass through the several stages of ovulation, fertilization, germination, and development, before it could maintain an independent existence. 3. That in their development they assumed but few primary structural patterns or types.

After the promulgation of the above doctrines, a series of investigations ensued, which brought naturalists to approximate a general agreement that there are only five general morphological or form-types of animals. Every animal, then, of the entire animal kingdom, must be classed in one or the other of these five sub-kingdoms, and each division thus classed has one fundamental plan of structure. The only way in which the animals of each sub-kingdom can differ is in the manner of executing their physiological functions.

In considering, then, any of the great physiological and philosophical questions that are based upon a uniformity of primitive type-development, we find that many useful lessons may be learned by including in our considerations every class of animals in which the specialization to be considered appears. For example, every animal belonging to the vertebrate sub-kingdom of animals agrees with every other animal of the same sub-kingdom in the following distinctive characteristics—characteristics, too, that we shall find involved in our considerations of the subject of the facial angle: In all, the head and vertebral column are composed of a number of definite segments, arranged along a longitudinal

Fig. 1.
PSM V04 D607 Cranial profiles.jpg

axis; each segment of this framework is normally composed of a body and two diverging, ring-like formations; the dorsal containing the brain and spinal cord, the ventral, or abdominal, containing the organs of nutrition, as the alimentary canal, circulating and eliminating organs. Every vertebrate animal, then, is possessed of two tubes of framework: the one, to protect the brain and spinal cord; the other, the organs of nutrition. These tubes are subject to very great variation, and are modified, as by a master's hand, to meet the necessities that their various specializations of function may demand. The great modification in the calibre of the dorsal tube in different classes of the vertebrates, as well as the great variation in shape of the elements which compose that arch, is apparent to every one. In the region of the spine, the elements that compose the segments of the arch are rounded, and at some distance apart, while in the cranial (skull) region they are flattened, spread out, so as to unite and form sutures, thus making a solid brain-case, for the protection of the softer and more massive nerve-matter.

The elements composing the nutritive case are the jaws, ribs, and pelvic girdle. These, like the spinal elements, are subject to great modification, owing to the immense range of variation to which their specializations are subjected. The difference in the facial developments

Fig. 2. Fig. 3.
PSM V04 D608 Cranial profiles.jpg

can well be imagined by calling to mind the various countenances of animals, from the fish to man. The angle of the face is simply and properly, I think, indicated by the relation expressed by two lines: the first, or base line, corresponding to the axis of the body; the other, diverging, or face line, drawn from the anterior margin of the upper jaw, over the centre of the forehead. The relation and angles formed by these two lines, and their intersections thus indicated, express the relation and comparative development at the union of the two primitive tubes, the neural, or skull, and hemal (face), at the anterior extremity or head of a vertebrate animal.

As before stated, authors have hitherto established the base-line from the floor of the nostrils, to the articulation of the occipital bone to the vertebra?. This is a grave error, and one, no doubt, that has contributed its share to depreciate the subject as an index to the mental caste of a vertebrate animal. For, by adopting this method, we are subject to the enormous error of ninety degrees in passing through the sub-kingdom, all of which we lose, little by little, as we ascend the scale of animals of this type, or form of structure. And yet they make this application through the entire vertebrate series. Yet, by referring to the cut, we find the face of the lowest class of the type, the fish, to be in direct line with the dorsal surface of the animal, and hence the base and diverging lines are parallel; while, in the highest of the type, that of man, the face is in line with the ventral or abdominal surface. Again, after effecting a grand variation of one hundred and eighty degrees, or the half of a circle, the two lines are once more parallel.

What, then, are the factors in the phenomena of the great change of the aspect of the face, with such a modification of its constituents, from a line of the dorsal to that of the abdominal surface, all of which is effected by almost imperceptible gradations, as we ascend the series from the fish to man? It is by the modification of the anterior extremities of these cranio-vertebral canals in the development and increase of the cerebral hemispheres, which is that part of the brain that is recognized as the seat of thought, and their influence upon other structures, that the whole change is wrought from a complete dominant power of the physical over the mental, to the reverse, viz., an entire dominant ascension, in some instances, of the moral and intellectual over the physical. In every vertebrate animal, then, there are two factors, the physical and mental; the facial angle is the typical expression or exponent of the relative strength or condition of each.

It may be observed that, with the ascension of these animals, the relative size of the brain-case, or skull, increases with a proportionate diminution of the bones of the face, and of the projection of the jaws in front of the orbits.

In the cold-blooded fish, the serpent, and the crocodile, the cavity for the brain is small, but little more than a prolongation of the canal for the spinal cord, with a disproportionate development of the organs of mastication, thus enabling them to execute the strongest instinct of the lower animals, namely, to slay and devour. In the bird class, the brain is somewhat larger, but is contained in the posterior part of the cranium, they manifesting but a slight mental superiority over the reptile. In the dog, over whom man is lord, and the noble horse, the brain is much larger; the facial line intersects at about a right angle with the base line, or vertebral axis. In these animals we begin to discover the rudiments of some of those more noble motives which are so abundantly lavished upon some of the higher animals.

The monkey and the anthropoid, or man-like apes, express in a very characteristic manner many of the mental attributes of the lower varieties of the human species. Nor is this to be wondered at, when we consider the close anatomical relation which subsists between the two, and the enormous development of the cerebral hemispheres as compared with the lower classes of the same type.

The profile of the idiot is the next introduced in the cut, to illustrate the Influence upon the size and shape of the cranium, or skull, that an arrest of brain-development has wrought, and which corresponds to the mental manifestations of its subject.

The other three profile views represent the savage, the half-civilized, and the cultivated races of man. The first of the three, the one next to the view of the idiot, is a drawing from a correct engraving of the celebrated North American Indian chief Black Hawk, and corresponds in brain capacity, facial angle, and mental powers, very nearly to the other savage races, viz., the Malayan and Ethiopian. The next that is represented in the cut is the half-civilized Mongolian race, illustrating very nicely the ratio of the two factors, physical and mental. The last is a representation of the highly-cultivated Caucasian race, and is a correct profile view of one of the most illustrious statesmen that this or any other nation ever possessed—that of Daniel Webster..

In the lowest of the type, the fish, we find the brain least developed, and the cerebral hemispheres, or instrument of thought, bearing the smallest proportion, either to its own concomitant structures, or to the rest of the body. The actual weight of a common codfish was 14,875 grains; the brain weighed only 9½ grains; thus making the ratio of 1 to 1,565. In man, the average weight of the brain is about 3 pounds, the medium weight of the body 150 pounds, making a ratio of 1 to 50. The above is a correct statement of the relative weight of the brain to the body of the lowest of the type, the fish, and the highest, man; showing the ratio of the weight of the brain in man, to that of the body, to be over 31 times greater than the same ratio in the fish. But, if we estimate the proportionate weight of merely the cerebral hemispheres, or the instruments of thought, to that of the body in the fish and man, we obtain a difference of 124, which expresses the number of times the cerebral hemispheres of man are greater than those of the fish; in other words, if the body of a fish and that of man were of equal weight, the cerebral hemispheres of the latter would weigh 124 times more than those of the former. Further, the relative weight of the cerebral hemispheres, as we ascend from the fish through the vertebrate sub-kingdom of animals, will be found to correspond to the variation of the face-line from a parallel with the dorsal surface.

To recapitulate: 1. The size and weight of the brain will be found to increase with the angle of the face to the axis of the body. 2. The expansion of the brain-case, with a proportionate diminution of the facial bones, is an invariable accompaniment of an increased facial angle throughout the vertebrate sub-kingdom of animals. 3. The mental manifestation and power have a direct relation to the angle above indicated. 4. The position assumed by the body of the animal in its change from the horizontal to the perpendicular attitude, also very generally agrees with the facial angle of its subject. 5. The projection of the jaws, in front of the ocular orbits, is also a correlative index to the above data. 6. The relative ascendency of the two factors, the physical and mental, with their numerous phenomena, is an index to all of the above relations, and shows very conclusively the gradual turning from the lowest instincts of the brute to the most complex mental powers of man.