No abstract

The recent detection of dermal ridge configurations on the volar pads of the rat (Rattus norvegicus) has created opportunities for experimental studies of dermatoglyphics. In the present work, the palmar and plantar surfaces of the rat were studied to establish the feasibility of comparative rat and human dermatoglyphic investigations. The studied features included the volar pads and flexion creases. The number and location of the palmar and plantar pads in the rat were found to be similar to those of humans. The exception was a previously unrecognized small pad on the palms and soles of the rat, located on the radial and tibial side, respectively, of the proximal component of the first interdigital pad. This pad has no parallel in human embryos. Rats were found to have flexion creases in the non-pad areas between the neighboring pads, similar in location and appearance to those of humans. Unlike humans, however, rats also have boundary creases, separating the pad and non-pad areas. The marked similarities in the morphology of the volar areas between rats and humans make the rat ideally suitable for experimental studies of dermatoglyphics and flexion creases. Results of such studies should be applicable to human developmental dermatoglyphics, including those pertaining to medical disorders.

A study of the embryological development and morphology of the thumb flexion creases is presented. We used 178 human fetuses, at 6-20 weeks of gestational age, and 225 normal adults, aged 19-81 years, to observe the morphology and the timing and location of the appearance of the flexion creases. Most creases, that is, the regular, extra, and oblique creases, were found to develop concurrently with the appearance of the fetal volar pads, apparently independently of the thumb flexion movements. Although the regular creases usually appear to be simple, single creases, they seem to be formed by the radial and ulnar lateral crease segments that develop inwards from each lateral side. Our observations also suggest that the oblique and extra creases on the proximal phalanx of the thumb should be considered as common or "regular" creases, rather than anomalies, because of their high frequency in fetuses and in normal healthy adults.

Reduced PCD interdigital tissue of Hm/+ and Hm/Hm fetuses may result in the failure of physiological elimination of interdigital cells and in the persistence of soft tissue webbing between digits. The failure of PCD to occur may also interrupt the interdigital surviving cells to reach the neighboring digits and the distal area of the palm, thereby producing ectopic dermal ridges. It seems that interdigital PCD contributes not only to digit separation but also to the development of digital and palmar pads.