Chapter 2. Prehension

208 THE PHASES OF PREHENSION
Epidermis
mine neaetoq du intermediate
dermal papillae
Figure 6.1 A schematic representation of the glabrous or hairless
skin of the human hand. Papillary ridges, also called primary or
sweat ridges, refer to the visible epidermal markings which leave
fingerprints. Note that the intermediate and limiting ridges of the
epidermis project down into the dermis, and that the primary and
secondary dermal papillae of the dermis project up into the
epidermis. The spiral ducts of the eccrine sweat glands coil their
way through the intermediate ridges and surface at the center tops
of the papillary ridges. The dermal papillae house Type I
cutaneous mechanoreceptors: Meissner corpuscles and Merkel
discs.
hairy and glabrous (nonhairy) skin (Montagna 8z Parakkal, 1974;
Quilliam, 1978). On the hand, these can be related to the demands for
grasping: the nonglabrous, dorsal skin is designed so as not to impede
flexion of the wrist and fingers. The glabrous skin (palmar) is
designed to comply, hold, resist pressure and shearing forces. The
epidermis is always thicker and the junction of the dermis and the
epidermis is much more complex in glabrous than in hairy skin. In
hairy skin, the demo-epidermal junction may be almost flat, except
for cones containing hair follicles. In contrast, in the glabrous skin of
the human hand, the interface between the dermis and the epidermis is
highly convoluted and interdigitated. The understructure of the
epidermis, unique in each part of the body, is irregular, with cones,
ridges and cords of different lengths, extending different depths into
the dermis. Thus the epidermis and dermis are tightly coupled; the