Preternatural position - situs mutatus, inversus, alienus, dislocatio, ectopia - is either congenital or acquired. In either case, it may affect a single organ or implicate several.

To congenital anomalies of the kind belong:

1. The Re-Establishment Of Symmetry

The Re-Establishment Of Symmetry, in lateral asymmetria. For example, each lung is found to have two lobes only, with both liver and heart in the centre. This is probably an arrest of development, these organs originally occupying the median line, and being in appearance symmetrically constituted.

2. Lateral Transposition

Lateral Transposition, displacement from side to side, affects either only individual organs of the thoracic or abdominal cavities - the caecum being, for instance, on the left, the heart on the right side; or else it affects the aggregate of the thoracic or of the abdominal viscera; or, lastly, and most commonly, the collective organs of both these cavities at once. The type of formation is reversed, the right greater lobe of the liver, for instance, becoming the left, the left becoming the right, the gall-bladder lying to the left of the longitudinal fissure. As regards the cause, it appears to Bischoff that in the embryo at an early period, the umbilical vesicle, after development of the intestine, verges towards the left, and the allantois towards the right, whereby a peculiar spiral revolution of the embryo is effected, which may possibly influence the position of the internal organs. It is conceivable that a change in the position of the germinal vesicle in the ovum might, in like manner, give rise to a transposition of organs.

3. Transposition From Above And Below

Thoracic organs in the abdomen; abdominal in the thorax.

4. Transposition From Front To Bach

Transposition From Front To Bach; for instance, in the case of teeth, in distortion of the extremities.

5. Displacement Of Individual Organs

Displacement Of Individual Organs from the median line, as for, instance, of the falx (cerebri), - of the uterus. Displacement upwards, as in cervical position of the heart. Displacement downwards, as in abdominal site of the heart, pelvic position of the kidneys.

Anomalous origin and distribution of arteries and veins. The more important examples hereof will be discussed under the head of special anomalies of the heart. They originate, for the most part, from bloodvessels which should have become further developed stopping short in their progress, whilst others which should have remained diminutive, or even have disappeared, persist and become more strongly developed. The majority represent types proper to different vertebrata - to fishes, amphibia, birds, and mammalia.

The preternatural position of certain organs which, in their development, undergo locomotion to a considerable extent, is specially termed deviation, aberration. An example offers in the descent of the testicle beneath the femoral arch or into the perinaeum. In truth, many anomalies of position are founded in an early aberration in this sense. The same designation is applied to anomalies in the origin, course, and ramification of vessels.

Acquired transposition is of various kinds, and many of these so closely resemble the congenital forms, as with difficulty to be distinguished from them. Their import varies greatly, proportionally to -

(a.) The importance of the organ displaced;

(6.) The number of organs displaced;

(c.) The extent of the displacement; and

(d.) Especially to the rapidity with which the dislodgment takes place, and to the corresponding strain upon various formations, more particularly bloodvessels and nerves.

(e.) The extent of the morbid compjication to which the displacement is due; for example, mechanical injury to the surrounding parts.

(/.) The degree of embarrassment to which the dislodged organs become subject; for instance, limitation of space, incarceration, exposure to the external air, etc.

(g.) The amount of functional embarrassment inflicted upon organs by the displaced parts; for example, upon the lungs by the intrusion of abdominal viscera into the thoracic cavity.

These transpositions are, moreover, spontaneous, where the organ changes its position owing to increase of volume, of mass, or of weight, in which case it commonly sinks into a lower region. Or else they depend upon conditions extraneous to the organ displaced; to which class belong dislodgments consequent upon atony of investing, supporting, attaching formations, especially when of a muscular and fibrous nature. Or they are referable to tonic spasm and retraction of fleshy, of tendinous, and of ligamentous formations, as exemplified in hernia, in curvature and distortion of the spine, in luxations, in club-foot, etc. Lastly, we have to mention the displacement of organs, through tumors, through dislodged or enlarged neighboring organs, through accumulated fluids, and the like.

The more important forms of displacement are:

1. Hernia

Hernia; the extrusion of one or more viscera, or of merely a portion of a viscus, out of its natural cavity into a sac formed by the circumscribed dilatation of the membranous investments of that cavity (hernial sac).

2. Prolapsus

Prolapsus; the naked extrusion of a viscus through a natural orifice. It is either complete or only partial; the former case occurs in hollow organs - for example, in the rectum, in the prolapsed and inverted womb. At an external opening of the body intussusception becomes prolapsus, which is intussusception minus the external layer or sheath.

3. Protrusion

Protrusion, propendentia, of viscera, owing to congenital fissure, or to rupture or penetrating wounds of the parietes of cavities.

Again, the position of organs may be anomalous, independently of any change of place, simply by preternatural inclination, especially in the shape of obliquity. This species of deviation is sometimes primitive and congenital, sometimes acquired. It affects the eye, the heart, the stomach, the uterus, the teeth, etc. It is frequently coupled with obliquity of form, as in the case of the uterus.