The sensory innervation of primate facial skin. II. Vermilion border and mucosa of lip

The study examined the sensory innervation of the vermilion border and mucosa of the monkey lip using light and electron microscopy. It found that Meissner corpuscles, which are similar to those in primate glabrous skin, were present at the junction between hairy skin and the vermilion border. These corpuscles were characterized by stacks of lamellae between loops of the terminal axon, with 1-3 myelinated axons innervating each corpuscle. Simple corpuscles were found in the non-keratinized portion of the vermilion border and oral mucosa, also innervated by 1-3 myelinated axons. The study noted a dense sensory innervation in these areas, correlating with the known tactile sensitivity of the lip. The findings suggested that the innervation of glabrous skin resembled that of hairy skin, with similar sensory terminals and structural units.