Sometimes the nails are exceedingly dense, or actually consist of several superimposed layers, so rich in pigment that they lose their characteristic transparency.
This condition is due to trophic disorders of the nails.
Teratology and Various Anomalies.—There are certain monstrosities that sometimes occur in connection with the hand, such as hexadactylism and polydactylism, or hands with six or more fingers; or else hands with less than five fingers—syndactylism. There may even be a congenital absence of a phalanx, with a consequent notable shortness of the finger—brachydactylism.
Another sort of anomaly frequently found in deficients consists of an excessive development of the interdigital membrane, to the extent of giving the hand the appearance of being web-fingered. An anomaly of minor importance consists in a distortion of the fingers; the little finger has one of its phalanges turned backward. All the fingers ought to be in contact throughout their whole length, and not leave open spaces between them.
Lines of the Palms.—The lines of the palms, which used to be of so much importance in chiromancy, are now taken into consideration even in anthropology, being studied in normal and abnormal man, and also in the hands of monkeys. The lines of the palms are three in number. The one which follows the curve of the tenar eminence is known in chiromancy as the line of life, and, if long, deep and unbroken, was supposed to denote good health and the prospect of a long life; in anthropology it is called the biological line. The second crease, which ought to meet the former between the thumb and the index-finger, is the line of the head, or cephalic line, and in chiromancy its union with the line of life was supposed to denote a well-balanced character.
The line highest up, which begins between the index- and middle finger and extends to the extreme margin of the palm, is the line of the heart or the cardiac line, which in chiromancy is supposed to indicate the emotional development of the individual. These lines taken together form a semblance of the letter M, and are characteristically and gracefully curved. It is considered as an anomaly, to be met with among degenerates and even in mongoloid idiots, to lack any of these lines (numerical reduction) or to have their arrangement distinctly horizontal, and reminiscent of the hand of the monkey.
If we trace backward in the zoological scale, we find as a matter of fact that to begin with, there were no lines in the palms, and then there appeared a single crease high up, such as we still find in the Cebus. In the human hand Carrara has recently made a study of these anomalies, distinguishing several types. In the first type there is a single transverse furrow. In the second type there are two furrows which, however, follow a definitely straight and horizontal direction and consequently are parallel. In a third type a single transverse furrow is associated with a very deep longitudinal furrow running from the carpus to the base of the index- and middle finger—a form that Carrara has found only in criminals. Nevertheless, many idiots exhibit a similar longitudinal furrow, due to a peculiar development of the palmar aponeurosis.
Fig. 129.—Imprint of human hand, showing papillary lines on palm and fingers.