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THE AMERICAN CATHOLIC

QUARTERLY REVIEW.

VOL. XI.-JULY, 1886.-No. 43.

THE SIGNIFICANCE OF ANATOMICAL ANOMALIES.

Les Anomalies Musculaires chez l'Homme expliquées par l'Anatomie Comparée-leur importance en Anthropologie. Par le Docteur L. Testut. Preface par M. le Prof. Duval. Paris, 1884. G. Masson.

IT

I.

T is a well-recognized fact that very frequently deviations from the usual structure are found in the human body. This is true of all the systems, of the bones, ligaments, muscles, bloodvessels, nerves, and of the internal organs. Sometimes the peculiarity is simply an increase or diminution in size of some particular muscle, artery, or bony prominence. Sometimes an artery or a nerve supplies by its branches a somewhat larger or smaller expanse than usual. Sometimes two neighboring muscles are more or less fused together, or the split that partially divides a muscle may be uncommonly deep. It is needless to say that, though the knowledge of these variations may sometimes be of great value to the surgeon, and that therefore they should be carefully studied, still they are of little scientific interest. But there are other variations of which this cannot be said, which, on the contrary, are of great importance on account of the bearing their interpretation may have on the great questions of the day. These are such as occasionally reproduce in the body of man forms of structure that are normal in the bodies of lower animals. It must not be sup

VOL. XI.-25

posed that the peculiarities referred to are of the nature of monstrosities or the result of morbid processes. For the most part they are not recognized during life, and have little or no influence for better or worse on the health of the individual. Before considering them in detail, let us glance at a few points in the structure and development of the bodies of man and of other vertebrate animals.

It is evident that they are built on the same general plan. They have a backbone, a spinal cord above it (in the upright position behind it) which enlarges in front (or above) into a brain. On the other side of the vertebral column are the digestive tract, the respiratory and circulatory systems. The extremities in all the higher animals are evidently modifications of the same type. Great as are the bodily differences between man and the nearest animals, they are differences of degree and not of kind.

When we examine the early embryonic stages of man and other mammals, the resemblance is increased. This is not in itself surprising, as it is but natural that the outlines of structure should appear first, and specific differences later; but what is very remarkable is that the embryos of higher animals present as transitory features structures that are permanent in lower ones. On the strength of this it has been asserted that the individual embryo rapidly runs through the changes that its ancestors have undergone in their progress up the zoological ladder. It is clear that this is assuming much more than we know. Not only does it beg the question of descent, but it is far from the demonstrated fact that it is passed off for. But however much the facts have been misinterpreted and the claims exaggerated, there remains something. We may at least say that the human embryo has certain transient features that are permanent in some lower animals.

In early stages of the vertebrate embryo the arteries make a series of arches in the neck closely resembling the permanent disposition of the main trunks in the gills of fishes. The minute openings which we sometimes see in the neck or about the ear of grown persons are explained as remnants of branchial clefts which once existed between these arteries. Of the five arterial arches on either side of the middle line, not necessarily existing at once, some remain pervious and some close up and disappear. Those that remain form the great vessels of the top of the chest and of the neck. Now in different classes of vertebrate animals, though the ground-plan is the same, the permanent arrangement is not. Thus in reptiles certain vessels remaining open form a double arch of the aorta, the great vessel that carries the blood from the heart; but in birds the vessel of one side is obliterated at an early period, so that there is but a single arch of the aorta which loops over the

right division of the windpipe. In mammals the vessel of the right side disappears and the aorta crosses the left air-tube.

Let us cite a few other examples relating to particular parts. The kidney in the human embryo is lobulated as in many animals, though it is smooth in the adult. Some muscles and tendons in the extremities have ape-like proportions. A certain fissure in the brain (the external parieto-occipital), which is well marked in apes, appears early in the human being and soon dwindles almost to nothing. Darwin laid much stress on the curious fact that the immature whalebone whale has teeth which never cut the gum and ultimately disappear.

These transitory stages being over and the animal having reached its adult state, there are found a number of so-called rudimentary organs, neither useful nor ornamental, which represent structures that have their uses in other species. These constitute a class of phenomena nearly allied to the anomalies that form the subject of this paper, but differing from them by being constant instead of only exceptionally present. The resemblance is the greater because these useless rudimentary organs are particularly prone to vary. A familiar example are the little ear muscles by which the shape of the outer ear may be changed in certain animals, but which in man are quite inert. Another instance is a thin layer of muscular fibres under the skin of the neck which represents a layer extending over most of the body by which many animals can wrinkle their skins so as to shake off insects or water. There is reason to believe that several other parts of the human body should be classed as rudimentary organs.

Let us now consider the body from another point of view. We have said that the bodies of vertebrate animals are built on a common plan, and the word "plan" was used advisedly. There is beyond question a certain symmetry and correspondence of parts in animals which is somewhat analagous to crystallization in inorganic matter. In vertebrates there is lateral symmetry or resemblance between the two sides, a serial homology between different segments of the body and between the extremities. Thus the shoulder and the hip, the arm and the thigh, the elbow and knee, the forearm and leg, the wrist and ankle, the hand and foot, evidently correspond in some way to one another. The precise nature of the correspondence between the limbs is a disputed point. Most authorities hold that the hind limbs are serial repetitions of the fore ones; others, that the front half of the body is to be compared to the hind half as the right is to the left, in which case it must be assumed that the homologue of the head remains rudimentary or is suppressed. A vast amount has been written on the subject. Attempts have been made to show homologies between

particular bones, muscles, arteries, and nerves according to various systems, and not a little confusion has resulted. In work of this kind the imagination must be kept well in hand. One considers with astonishment what utter trash has been written by really able men, bringing undeserved discredit on this field of research. The truth has been hidden by exaggerations. Because transcendental anatomists wrote nonsense, many have over hastily assumed that the underlying idea is a delusion. The trouble has been that the transcendentalists attempted too much. The data were wanting for even much more general comparisons than they instituted. No unbiassed mind, however, can fail to recognize symmetry in the individual and homology in different species. The arm is very different in man, the tiger, the horse, the bat, the seal, the eagle, the penguin, and the turtle; but in each of these there is an evident correspondence of parts with those in others and also with those in the hind limb of the same animal.

II.

Let us now pass in review some of the anomalies that are occasionally found in man. Very rarely a knob is seen projecting downward from the under surface of the base of the skull near the spine. Most books on human anatomy say nothing of it, and the student who knows nothing of comparative anatomy would be quite at a loss to account for it; but it represents a structure found in many mammals. It is greatly developed in several of the ungulata, as the sheep, the horse, the rhinoceros, etc. Again we occasionally meet with a hook-like bony excrescence from the humerus, a little above the inner side of the elbow, from which a fibrous band makes a bridge over an opening which corresponds to a hole in the bone in some apes, in some carnivora, and in some species of other orders through which an important nerve and artery pass. It is generally taught that this arrangement serves to protect these structures from pressure during the long continued contraction of some of the muscles. Be that as it may, if it is of any use in man, which may be doubted, the favored possessors of this structure are few and far between. Some authorities state that it occurs about three times in a hundred, but the writer's experience leads him to believe that it is much rarer. Remarkable anomalies are found in the large bloodvessels (those in the small are too numerous to discuss) depending on the irregular persistence or closure of the branchial arteries already mentioned. Sometimes the aorta arches over the right bronchus, as in birds, sometimes there is a double arch, as in reptiles.

Anomalies of the muscular system are very numerous and in