HETEROTAXY.
Heterotaxy includes simple changes in the position of organs, and such changes often occur without real alteration in the relations and connec tions; in other words they are complex and yet do not at all interfere with the function of the organs. (Saint-Hilaire.) This author recognizes two special divisions: In the one the external form of the individual is pre served, the malformation being limited to the viscera; in the other the entire individual is affected, as well the external as the internal organs. This form is only met with in animals, and not in man, where the two halves of the body are symmetrical. It should not, therefore, detain us.
Inversion of the internal viscera may be total or partial—total when all the abdominal thoracic viscera are affected, partial when only a few.
Total Inversion of the reported cases are numerous enough. All the viscera are displaced, although retaining their normal connections. Analogically, indeed, " the relation is as the wood-cat to the proof." What is the cause of inversion? In the embryo the majority of the viscera are symmetrical, and if a certain number become later asymmetrical, this may depend on a number of causes. Of the
organs which are double in the beginning and situated on each side of the median line, one may disappear and the other persist. If the organ which should atrophy persists, and the one which should persist atrophies, inversion will exist. For instance, hepatic inversion would result if the right lobe should atrophy and the left hypertrophy, these two lobes being considered as remnants of two livers. Again, normally, the digestive tube is single, situated in the mid-line, and its right and left halves are symmetrical. The tube may curve and its dimensions become modified, the stomach forming a right angle with the oesophagus. Thus primitive -symmetry would be destroyed.
Partial inversion of the Viscera.—This variety is rare. It may be limited to the lungs. As instances we note anomalies in distribution of the great vessels at the base of the heart, anomalies in position of the heart.