Although monstrosities, both in the human species and in other animals, tend to repeat certain definite types of erroneous development, they do not fall readily into classes. It is remarked by Vrolik that a scientific classification is impracticable from being too cumbrous, and that a convenient grouping is all that need be attempted. The most usual grouping (originally suggested by Buffon, 1800) is into monstra per excessum, monstra per defectum, and monstra per fabricam alienam. It seems useful, however, to place the more simple cases of excess and of defect side by side; and it is necessary, above all, to separate the double monsters from the single, the theory of the former being a distinct chapter in teratology.

1. Monstrosities in a Single Body.— The abnormality may extend to the body throughout, as in well-proportioned giants and dwarfs; or it may affect a certain region or member, as—to take the simplest case—when there is a finger or toe too many or too few. It is very common for one malformation to be correlated with several others, as in the extreme case of acardiac monsters, in which the non-development of the heart is associated with the nondevelopment of the head, and with other radical defects.

Giants are conventionally limited to persons over 7 feet in height. The normal proportions of the frame are adhered to more or less closely, except in the skull, which is relatively small; but accurate measurements, even in the best-proportioned cases, prove, when reduced to a scale, that other parts besides the skull, notably the thigh-bone and the foot, may be undersized though overgrown. In persons who are merely very tall, the great stature depends often on the inordinate length of the lower limbs; but in persons over 7 feet the lower limbs are not markedly disproportionate. In many cases the muscles and viscera are not sufficient for the overgrown frame, and the individuals are usually, but not always, of feeble intelligence and languid disposition, and short-lived. The brain-case especially is undersized—the Irish giant in the museum of Trinity College, Dublin, is the single exception to this rule—but the bones of the face, and especially the lower jaw, are on a large scale. Giants are never born of gigantic parents; in fact, sterility usually goes with this monstrosity. Their size is sometimes excessive at birth, but more often the indications of great stature do not appear till later, it may be as late as the ninth year; they attain their full height before the twenty-first year. They have been more frequently male than female; the German giantess lately exhibited (1882) was as tall as any authentic case in the male sex.

Dwarfs are conventionally limited to persons under 4 feet. They are more likely than giants to have the modulus of the body perfect. “In the true dwarf, as far as I have been able to ascertain, the proportions between the several parts of the frame are good, corresponding, or nearly corresponding, with those of the normal adult; and the diminutive stature depends, accordingly, not upon relatively imperfect growth of any particular segments, or even upon the permanence of a foetal or childlike condition, but upon the whole frame being undersized” (Humphry). Where disproportion occurs in the true dwarf it takes the form of a large-sized head, broad shoulders and capacious chest, and undersized lower limbs. Dwarfs with rickets are perhaps to be distinguished from true dwarfs; these are cases in which the spine is curved, and sometimes the bones of the limbs bent and the pelvis deformed. As in the case of giants, dwarfs are seldom the progeny of dwarfs, who are, in fact, usually sterile; the unnatural smallness may be obvious at birth, but is more likely to make itself manifest in the years of growth. Dwarfs are much more easily brought up than giants, and are stronger and longer-lived; they have usually also strong passions and acute intelligence. The legends of the dwarfs and giants are on the whole well based on fact (see Dwarf and Giant). Redundancy and Defect in Single Parts.— The simplest case of this redundancy is a sixth digit, well formed, and provided with muscles (or tendons), nerves, and bloodvessels like the others; it is usually a repetition of the little finger or toe, and it may be present on one or both hands, or on one or both feet, or in all four extremities, as in the giant of Gath. The want of one, two, or more digits on hand or foot, or on both, is another simple anomaly; and, like the redundancy, it is apt to repeat itself in the same family. Meckel saw a girl who had an extra digit on each extremity, while a sister wanted four of the fingers of one hand. Where the supernumerary digits are more than one on each extremity, the whole set are apt to be rudimentary or stunted; they look as if two or more of the embryonic buds had been subject to cleavage down the middle, and to arrest of longitudinal growth. There are two or three authentic instances of a whole lower limb appearing at birth as two withered halves, as if from embryonic cleavage. Other redundancies of the skeleton are extra vertebrae (sometimes the coccygeal, giving the appearance of a rudimentary tail), or an extra rib. A double row of teeth is occasionally met with; the most interesting case of this anomaly is that in which the rudiments of a double row exist from the first, but the phenomenon is sometimes produced by the milk teeth persisting along with the second set. One or more extra teeth are occasionally met with in line with the rest. Among redundancies of the soft parts, by far the most frequent is an extra nipple, or pair of nipples. It is only the nipple, or the most external mechanical adjunct of the mammary apparatus, that is repeated, and very seldom, if ever, the breast structure itself. The nipple, although it is the latest addition to the mechanism of lactation, is in the individual mammal developed on the skin before the gland is formed underneath; and that facility, which applies to the development of external characters generally, appears to be the reason why there may be one or more extra nipples but no redundant gland. In the same connexion, it is interesting to observe that the supernumerary nipple has been shown by statistics on a large scale to be twice as common in men as in women, although in the male the mammary function never comes to maturity, and even the structure retrogrades after puberty. Traces of an additional nipple, or pair of them, in more or less symmetrical position below the normal ones, are not very uncommon when carefully looked for. Among the sense organs there is a remarkable instance recorded of doubling of the appendages of the left eye, but not of the eyeball itself; the left half of the frontal bone is double, making two eye-sockets on that side, and the extra orbit has an eyebrow and eyelid. The external ear (pinna) has also been found double on one side. Doubling of any of the internal organs is extremely rare, and is probably always traceable to a more or less complete fissuring or lobation. The ducts or vessels connected with organs, and playing a purely mechanical part, are not unfrequently doubled; thus each kidney may have two ureters, and a similar variation may occur in veins and arteries.

Monstrosities from Defective Closure in the Middle Line.— Under this head come some of the commonest congenital malformations, including slight deficiencies such as harelip, and serious defects such as a gap in the crown of the head with absence of the brain. The embryo is originally a circular flattened disc spread out on one pole of the yolk, and it is formed into a cylindrical body (with four appendages) by the free margins of the disc, or rather its ventral laminae, folding inwards to meet in the middle line and so close in the pelvic, abdominal, thoracic, pharyngeal, and oral cavities. Meanwhile, and indeed rather earlier, two longitudinal parallel ridges on the top or along the back of the disc have grown up and united in the middle line to form the second barrel of the body—the neural canal—of small and uniform width in the lower three-fourths or spinal region, but expanding into a wide chamber for the brain. This division into neural (dorsal) and haemal (ventral) canals underlies all vertebrate development. Imperfect closure along either of those embryonic lines of junction may produce various degrees of monstrosity. The simplest and commonest form, hardly to be reckoned in the present category, is harelip with or without cleft palate, which results from defective closure of the ventral laminae at their extreme upper end. Another simple form, but of much more serious import, is a gap left in the neural canal at its lower end; usually the arches of the lumbar vertebrae are deficient, and the fluid that surrounds the spinal cord bulges out in its membranes, producing a soft tumour under the skin at the lower part of the back. This is the condition known as hydrorhachis, depending on the osseous defect known as spina bifida. Children born with this defect are difficult to rear, and are very likely to die in a few days or weeks. More rarely the gap in the arches of the vertebrae is in the region of the neck. If it extend all along the back, it will probably involve the skull also. Deficiency of the crown of the head, and in the spine as well, may be not always traceable to want of formative power to close the canal in the middle line; an over-distended condition of the central water-canal and water-spaces of the cord and brain may prevent the closure of the bones, and ultimately lead to the disruption of the nervous organs themselves; and injuries to the mother, with inflammation set up in the foetus and its appendages, may be the more remote cause. But it is by defect in the middle line that the mischief manifests itself, and it is in that anatomical category that the malformations are included. The osseous deficiency at the crown of the head is usually accompanied by want of the scalp, as well as of the brain and membranes. The bones of the face may be well developed and the features regular, except that the eyeballs bulge forward under the closed lids; but there is an abrupt horizontal line above the orbits where the bones cease, the skin of the brow joining on to a spongy kind of tissue that occupies the sides and floor of the cranium. This is the commonest form of an anencephalous or brainless monster. There are generally mere traces of the brain, although, in some rare and curious instances, the hemispheres are developed in an exposed position on the back of the neck. The cranial nerves are usually perfect, with the exception sometimes of the optic (and retina). Vegetative existence is not impossible, and a brainless monster has been known to survive sixty-five days. The child is usually a very large one.

Closely allied, as we have seen, to the anencephalous condition is the condition of congenital hydrocephalus. The nervous system at its beginning is a neural canal, not only as regards its bony covering, but in its interior; a wide space lined by ciliated epithelium and filled with water extends along the axis of the spinal cord, and expands into a series of water-chambers in the brain. As development proceeds, the walls thicken at the expense of the internal water-spaces, the original tubular or chambered plan of the central nervous system is departed from, and those organs assume the practically solid form in which we familiarly know them. If, however, the water-spaces persist in their embryonic proportions notwithstanding the thickening of the nervous substance forming their walls, there results an enormous brain which is more than half occupied inside with water, contained in spaces that correspond on the whole to the ventricles of the brain as normally bounded. A hydrocephalic foetus may survive its birth, and will be more apt to be affected in its nutrition than in its intelligence. In many cases the hydrocephalic condition does not come on till after the child is born. The microcephalous condition, where it is not a part of cretinism, is not usually a congenital defect in the strict sense, but more often a consequence of the premature union of the bones of the skull along their sutures or lines of growth.

Returning to the ventral middle line, there may be defects of closure below the lips and palate, as in the breast-bone (fissure of the sternum), at the navel (the last point to close in any case), and along the middle line of the abdomen generally. The commonest point for a gap in the middle line of the belly is at its lower part, an inch or two above the pubes. At that point in the embryo there issues the allantois, a balloon-like expansion from the ventral cavity, which carries on its outer surface blood-vessels from the embryo to interdigitate with those of the mother on the uterine surface. Having served its temporary purpose of carrying the blood-vessels across a space, the balloon-like allantois collapses, and rolls up into the rounded stem-like umbilical cord through most of its extent; but a portion of the sac within the body of the foetus is retained as the permanent urinary bladder. That economical adaptation of a portion of a vesicular organ, originally formed for purposes of communication between the embryo and the mother, appears to entail sometimes a defect in the wall of the abdomen just above the pubes, and a defect in the anterior wall of the bladder itself. This is the distressing congenital condition of fissure of the urinary bladder, in which its interior is exposed through an opening in the skin; the pubic bones are separated by an interval, and the reproductive organs are ill formed; the urachus is wanting, and the umbilicus is always placed exactly at the upper end of the gap in the skin. A monstrosity recalling the cloacal arrangement of the bird is met with as a more extreme defect in the same parts.

Hermaphroditism,. — Although this anomalous condition does not fall under defective closure in the middle line, it may be said to be due to a similar failure of purpose, or to an uncertainty in the nisus formativus at a corresponding stage of development. There is a point of time, falling about the eighth week, up to which the embryo may develop either the reproductive organs of the male or the reproductive organs of the female; in the vast majority of cases the future development and growth are carried out on one line or the other, but in a small number there is an ambiguous development leading to various degrees of hermaphroditism or doubtful sex. The primary indecision, so to speak, affects only the ovary or testis respectively, or rather the common germinal ridge out of which either may develop; the uncertainty in this embryonic sexual ridge sometimes leads actually to the formation of a pair of ovaries and a pair of small testes, or to an ovary on one side and a testis on the other; but even when there is no such double sex in the essential organs (as in the majority of hermaphrodites) there is a great deal of doubling and ambiguity entailed in the secondary or external organs and parts of generation. Those parts which are rudimentary or obsolete in the male but highly developed in the female, and those parts which are rudimentary in the female but highly developed in the male tend in the hermaphrodite to be developed equally, and all of them badly. In some cases the external organs of one sex go with the internal organs of the opposite sex. It has been observed that when middle life is reached or passed the predominance in features, voice, and disposition leans distinctly towards the masculine side. The mythological or classical notions of hermaphroditism, like so much else in the traditions of teratology, are exaggerated.

Cyclops, Siren, Ac. — The same feebleness of the formative energy (the Bildungstrieb of Blumenbach) which gives rise to some at least of the cases of defective closure in the middle line, and to the cases of undecided sex, leads also to imperfect separation of symmetrical parts. The most remarkable case of the kind is the cyclops monster. At a point corresponding to the root of the nose there is found a single orbital cavity, sometimes of small size and with no eyeball in it, at other times of the usual size of the orbit and containing an eyeball more or less complete. In still other cases, which indicate the nature of the anomaly, the orbital cavity extends for some distance on each side of the middle line, and contains two eyeballs lying close together. The usual nose is wanting, but above the single orbital cavity there is often a nasal process on the forehead, with which nasal bones may be articulated, and cartilages joined to the latter; these form the framework of a short fleshy protuberance like a small proboscis. The lower jaw is sometimes wanting in cyclopeans; the cheek-bones are apt to be small, and the mouth a small round hole, or altogether absent; the rest of the body may be well developed. The key to the cyclopean condition is found in the state of the brain. The olfactory nerves or lobes are usually described as absent, although Vrolik has found them in some instances; the brain is very imperfectly divided into hemispheres, and appears as a somewhat pear-shaped sac with thick walls, the longitudinal partition of dura mater (falx cerebri) being wanting, the surface almost unconvoluted, the corpus callosum deficient, the basal ganglia rudimentary or fused. The optic chiasma and nerves are usually replaced by a single mesial nerve, but sometimes the chiasma and pair of nerves are present. The origin of this monstrosity dates back to an early period of development, to the time when the future hemispheres were being formed as protrusions from the anterior cerebral vesicle or fore-brain; it may be conceived that, instead of two distinct buds from that vesicle, there was only a single outgrowth with imperfect traces of cleavage. That initial defect would carry with it naturally the undivided state of the cerebrum, and with the latter there would be the absence of olfactory lobes and of a nose, and a single eyeball placed where the nose should have been. A cyclops has been known to live for several days. The monstrosity is not uncommon among the domestic animals, and is especially frequent in the pig. There is another congenital malformation, in which an eyeball is wanting from one of the sockets; but in that case there is no defect of development in the bones, and the brain and nose are normal.

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