The fine structure of the digital corpuscle of the mouse toe pad, with special reference to nerve fibers.

Digital corpuscles in the dermal papillae of the mouse toe pad have been studied using light and electron microscopy of serial thick and thin sections, and silver impregnations of frozen sections. These corpuscles are ellipsoid in shape and approximately 10-30 mum in diameter. They consist of one to three lamellar cells, nerve fibers and a capsule. These digital corpuscles are regarded as small Meissner corpuscles. The capsule is perineural epithelium. One or two myelinated nerve fibers and occasionally an unmyelinated nerve fiber enter the corpuscle. The axon terminals contain many mitochondria and a variable population of vesicular profiles. These terminals are ellipsoid or discoid in shape with the long axis parallel to the skin surface. The cytoplasmic plates (or lamellae) of the lamellar cells are arranged parallel to the skin surface, as is the cleft between the bilaterally symmetrical stacks of lamellae. Small processes extend from the expanded terminal of the neurite into the cleft between the lamellae. The relationship of the neurite terminal and associated lamellar cells resembles in some respects the organization of the inner core of Pacinian corpuscles. Intraepidermal fibers derived from myelinated neurites of the corpuscle may extend to the superficial epidermis. Intraepidermal fibers derived from unmyelinated neurites usually terminate in the basal regions of the epidermis.