And Monstrositas, (from monstro, to show). Monster, or a monstrous, i. e. a preternatural production.

A monster is very judiciously defined by Dr. Hamilton, in his valuable and comprehensive Outlines, to consist in"any considerable deviation in the structure of the foetus from the common order of nature, whether such deviation be consistent with life or not."

Monsters, according to the same author, are, 1st, those which are double, or have supernumerary parts; 2dly, those who have a deficiency of some organ; 3dly, those who have any remarkable deviation either in the situation of the viscera, the distribution of the vessels, nerves, or secretory organs, though not externally visible, or materially affecting the different functions; 4thly, the productions of animals of different species.

Monsters double, or with supernumerary organs, have been often described. The Bohemian sisters, united by the glutaei muscles, with a more intimate connection in the abdominal viscera, are well known to physiologists. The monster, mentioned in the Philosophical Transactions (No. 2), consisted of two bodies equally distinct, and in various other parts of this collection there are cases where the union is more or less complete. This double form gradually sinks to the child growing from the side of another, recorded in the Asiatic Transactions, down to the double head of the Hindoo child, in Mr. Hunter's collection. Supernumerary organs are very frequent, and this peculiarity is at times confined to particular families. It is remarkable that the peculiarity will disappear for one, and sometimes two, generations, reviving again in the third. The internal organs are occasionally double or supernumerary. The most singular case of this kind is where two hearts were discovered.

Deficiencies are also numerous. A head, an eye, an arm, a leg, a hand, foot, or finger, are sometimes wanting; but the chief deficiency, which calls for our attention is that of the head. This has occasioned many speculations; but in every instance there is a point at which all the nerves converge, or from which they proceed, and this contains very generally a cortical, or a nucleus of cineritious, matter. We may, however, remark as a fact of future application, that the acephalous children are often plump, and of no diminutive size; yet the instance has escaped us, if any has occured, where such children are not in other respects monstrous. The vital organs must be always, to a certain degree, perfect: at least neither the heart nor the large vessels can be wanting in a child which has arrived at its full time.

The third instance of monstrosity is rare, or at least rarely ascertained. We have instances on record of the viscera being on the sides opposite to those in which they are usually placed, and the pulmonary vessels are occasionally defective, or useless from the foetal passages continuing open. From the last cause chiefly arises the caerulian complexion of some children. Various are the changes which may occasionally take place in the distribution of the vessels, the situation of the glands, or the direction of the nerves within the limits of health; and numerous must necessarily be the instances in which these irregularities have not been observed. The imperfection of natural passages is scarcely sufficient to arrange such persons under the rank of monsters. It is a disease of structure, which merits no such appellation, and we have anxiously excluded them by our definition.

The productions of animals of different species are rare; and these very seldom, if ever, fertile. Providence has thus wisely preserved every species distinct, and the world is not peopled with monsters. Yet, among animals of the larger size, which usually produce only a single offspring, twins are rarely, both, perfect. This, however, is not the case in man, or in the lower orders of animals. We only see it distinctly in the cow.

In the vegetable kingdom, we find monsters produced by excess of nourishment, or by the opposite extreme of confinement and deficient nutriment. To the former we attribute the double unfertile flowers; to the latter the variegated leaves of plants. We are not without similar instances in the human species. The full plethoric female is seldom a mother of many children, and the Laplander, the Esquimaux, and the Cretin are deformed in their bodies, and imperfect in their intellectual faculties. They have not, however, been distinguished by the appellation of monsters.

To what are these deviations from the common structure owing ? We have endeavoured to render the pre-existence of the germ in the female constitution probable; and the monstrosities observable in succeeding generations are owing probably to the imperfect germ. Where, however, parts are double, or the deviations from the common structure are considerable, we cannot admit this source. M. Lemery long since contended that monsters were rendered such by accidents in the uterus. Winslow supported the idea of Duverney, who supposed the germ to have been monstrous, and first started this opinion. Each opinion has been supported with great obstinacy by their respective authors, in the Memoiresde lacademie des Sciences, An. 1728, 1740, 1742, and 1743.

The double children are certainly such as from contiguity have accreted in their tenderest state. We can have no doubt of this in the instances recorded in the Philosophical Transactions, where they ate and slept at different hours; where their excretions and tempers were distinct and discriminated. If it be the case in these instances, may we not suppose that, by a stricter approximation, some of the abdominal viscera may be so closely pressed as to destroy the parietes on the weaker side, and the canals to be consequently common? This was the case with the Bohemian sisters. Again, may not a more partial and a stronger pressure obliterate even the lower extremities of the weaker child, and the trunk inosculate with that of the stronger, as in the case recorded by Dr. Bland in the Philosophical Transactions ? and may not a similar cause, in twins greatly disproportioned in strength, account for all the varieties of a child growing out of the side, down to the double head of the Hindoo, or even the double heart ? It was not from accident that we said disproportioned strength; for the double portion is usually small and imperfect.

It is not possible to follow all the varieties. While we have admitted, at one extreme, the monstrous germ, we have endeavoured to support, at the opposite, the effects of pressure. We can go no farther. Where the limits of either cause may be, is uncertain; nor is it necessary to follow doubtful and unsteady lights in a track which leads to no useful purpose. One thing we may add, that inno instance is it probable that deficient or redundant monsters are owing to the fright of the mother, or disgusting objects presented to her.

The absurdities that crowd the pages of Schenkius, Bartholine, AElian, De Reies, Vanderwiel, Paulini, etc. down to our own rabbit woman, and Roederer's relation of a female that brought forth a fish, must not detain us. It is enough to have stated the several facts, and to have made some approaches towards an explanation.

Philosophical Transactions, No. 2, 99, 226, 228, 234,251,308, 320, 453, 456, 487, & c.; Medical and Physical Journal, Passim; Memoires de l 'academie des Sciences, An. 1724, 1738 - 43; Mauriceau, Smellie, and De la Motte's Midwifery; Journal de Physique, An. 1774, and 1776. See Acephalos and Praesen-tatio.